[C++11] Replacing iterators redecls_begin() and redecls_end() with iterator_range redecls(). Updating all of the usages of the iterators with range-based for loops, which allows the begin/end forms to be removed entirely.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203179 91177308-0d34-0410-b5e6-96231b3b80d8