DI: Remove unnecessary DICompositeTypeBase

Remove unnecessary and confusing common base class for `DICompositeType`
and `DISubroutineType`.

While at a high-level `DISubroutineType` is a sort of composite of other
types, it has no shared code paths, and its fields are completely
disjoint.  This relationship was left over from the old debug info
hierarchy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243160 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed