[TableGen][NFC] Remove unreachable code

The removed code assumed that we can define classes inside a multiclass,
so the name of outer multiclass is concatenated to the qualified name.
But for current TableGen grammar, we can't define classes in multiclass,
so it is unnecessary.

This commit is requested in D152998.

llvm/lib/TableGen/TGParser.cpp

@@ -117,11 +117,6 @@ static Init *QualifyName(Record &CurRec, MultiClass *CurMultiClass, Init *Name,
   Init *NewName = BinOpInit::getStrConcat(CurRec.getNameInit(),
                                           StringInit::get(RK, Scoper));
   NewName = BinOpInit::getStrConcat(NewName, Name);
-  if (CurMultiClass && Scoper != "::") {
-    Init *Prefix = BinOpInit::getStrConcat(CurMultiClass->Rec.getNameInit(),
-                                           StringInit::get(RK, "::"));
-    NewName = BinOpInit::getStrConcat(Prefix, NewName);
-  }
 
   if (BinOpInit *BinOp = dyn_cast<BinOpInit>(NewName))
     NewName = BinOp->Fold(&CurRec);