[MemorySSA] MemorySSA should not model debuginfo, and need not update it.

Reverts the change in r371084, but keeps the test.
After r371565, debuginfo cannot be modelled in MemorySSA, even with a
non-standard AA pipeline.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@371573 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -250,11 +250,8 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
       llvm::findDbgValues(DbgValues, Incoming);
       for (auto &DVI : DbgValues) {
         auto R = DbgValueSet.insert({DVI->getVariable(), DVI->getExpression()});
-        if (!R.second) {
-          if (MSSAU)
-            MSSAU->removeMemoryAccess(DVI);
+        if (!R.second)
           DVI->eraseFromParent();
-        }
       }
     }
   }