Revert r222965 "Make MultiClass::DefPrototypes own their Records to fix memory leaks."

The bots started failing with the error below. I suspect this revision was the cause.

FAILED: /home/bb/bin/g++47   -DGTEST_HAS_RTTI=0 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -ffunction-sections -fdata-sections -O3 -DNDEBUG -Ilib/TableGen -I/home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen -Iinclude -I/home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include    -fno-exceptions -fno-rtti -MMD -MT lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGParser.cpp.o -MF "lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGParser.cpp.o.d" -o lib/TableGen/CMakeFiles/LLVMTableGen.dir/TGParser.cpp.o -c /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.cpp
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_tempbuf.h:62:0,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_algo.h:64,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/algorithm:63,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include/llvm/ADT/StringRef.h:13,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGLexer.h:17,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.h:17,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.cpp:14:
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_construct.h: In instantiation of 'void std::_Construct(_T1*, _Args&& ...) [with _T1 = std::unique_ptr<llvm::Record>; _Args = {const std::unique_ptr<llvm::Record, std::default_delete<llvm::Record> >&}]':
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_uninitialized.h:77:3:   required from 'static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<llvm::Record>*, std::vector<std::unique_ptr<llvm::Record> > >; _ForwardIterator = std::unique_ptr<llvm::Record>*; bool _TrivialValueTypes = false]'
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_uninitialized.h:119:41:   required from '_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<llvm::Record>*, std::vector<std::unique_ptr<llvm::Record> > >; _ForwardIterator = std::unique_ptr<llvm::Record>*]'
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_uninitialized.h:260:63:   required from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = __gnu_cxx::__normal_iterator<const std::unique_ptr<llvm::Record>*, std::vector<std::unique_ptr<llvm::Record> > >; _ForwardIterator = std::unique_ptr<llvm::Record>*; _Tp = std::unique_ptr<llvm::Record>]'
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_vector.h:310:9:   required from 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = std::unique_ptr<llvm::Record>; _Alloc = std::allocator<std::unique_ptr<llvm::Record> >]'
/home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include/llvm/TableGen/Record.h:1664:8:   required from 'constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&) [with _U1 = std::basic_string<char>&; _U2 = llvm::MultiClass; <template-parameter-2-3> = void; _T1 = std::basic_string<char>; _T2 = llvm::MultiClass]'
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_pair.h:273:72:   required from 'constexpr std::pair<typename std::__decay_and_strip<_T1>::__type, typename std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&) [with _T1 = std::basic_string<char>&; _T2 = llvm::MultiClass; typename std::__decay_and_strip<_T2>::__type = llvm::MultiClass; typename std::__decay_and_strip<_T1>::__type = std::basic_string<char>]'
/home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.cpp:2295:78:   required from here
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/stl_construct.h:77:7: error: use of deleted function 'std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = llvm::Record; _Dp = std::default_delete<llvm::Record>]'
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/memory:86:0,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include/llvm/ADT/STLExtras.h:25,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include/llvm/ADT/ArrayRef.h:14,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/include/llvm/Support/SourceMgr.h:19,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.h:19,
                 from /home/bb/cmake-llvm-x86_64-linux/llvm-project/llvm/lib/TableGen/TGParser.cpp:14:
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/unique_ptr.h:262:7: error: declared here
ninja: build stopped: subcommand failed.