Sink DwarfUnit::CURanges into DwarfCompileUnit

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221161 91177308-0d34-0410-b5e6-96231b3b80d8
Cleanup some unused or trivial functions in DwarfCompileUnit

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221164 91177308-0d34-0410-b5e6-96231b3b80d8