[Modules] Sink the DEBUG_TYPE macro out of LegalizeTypes.h and into the
various .cpp files. This macro is inherently non-modular, and it wasn't
even needed in this header file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206775 91177308-0d34-0410-b5e6-96231b3b80d8