DebugInfo: Remove DIDescriptor::Verify()

Remove `DIDescriptor::Verify()` and the `Verify()`s from subclasses.
They had already been gutted, and just did an `isa<>` check.

In a couple of cases I've temporarily dropped the check entirely, but
subsequent commits are going to disallow conversions to the
`DIDescriptor`s directly from `MDNode`, so the checks will come back in
another form soon enough.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234201 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -637,8 +637,6 @@ DwarfCompileUnit::constructAbstractSubprogramScopeDIE(LexicalScope *Scope) {
 
 std::unique_ptr<DIE>
 DwarfCompileUnit::constructImportedEntityDIE(const DIImportedEntity &Module) {
-  assert(Module.Verify() &&
-         "Use one of the MDNode * overloads to handle invalid metadata");
   std::unique_ptr<DIE> IMDie = make_unique<DIE>((dwarf::Tag)Module.getTag());
   insertDIE(Module, IMDie.get());
   DIE *EntityDie;