DebugInfo: Delete old subclasses of DIType

Delete subclasses of (the already deleted) `DIType` in favour of
directly using pointers from the `Metadata` hierarchy.

While `DICompositeType` wraps `MDCompositeTypeBase` and `DIDerivedType`
wraps `MDDerivedTypeBase`, most uses of each really meant the more
specific `MDCompositeType` and `MDDerivedType`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235351 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1902,7 +1902,7 @@ static uint64_t makeTypeSignature(StringRef Identifier) {
 
 void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
                                       StringRef Identifier, DIE &RefDie,
-                                      DICompositeType CTy) {
+                                      const MDCompositeType *CTy) {
   // Fast path if we're building some type units and one has already used the
   // address pool we know we're going to throw away all this work anyway, so
   // don't bother building dependent types.