Drop: assertion too strict for revng usecase

IRmover asserts that a two types into two modules can be pointer wise
identical only if they are mapped to each other. This assumption arise
from the idea that modules are usually created indipendently from each
other.

We cannot make that assumption because the pipeline clones and merges
back modules from the same origin.

Author: drblallo

llvm/lib/Linker/IRMover.cpp

@@ -243,13 +243,6 @@ Type *TypeMapTy::get(Type *Ty, SmallPtrSet<StructType *, 8> &Visited) {
   bool IsUniqued = !isa<StructType>(Ty) || cast<StructType>(Ty)->isLiteral();
 
   if (!IsUniqued) {
-#ifndef NDEBUG
-    for (auto &Pair : MappedTypes) {
-      assert(!(Pair.first != Ty && Pair.second == Ty) &&
-             "mapping to a source type");
-    }
-#endif
-
     if (!Visited.insert(cast<StructType>(Ty)).second) {
       StructType *DTy = StructType::create(Ty->getContext());
       return *Entry = DTy;