DebugInfo: Remove DW_TAG_constant

Remove handling for DW_TAG_constant.  We started producing it in
r110656, but reverted that in r110876 without dropping the support.
Finish the job.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228623 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed