[InstCombine] Don't explicitly invoke const folding in shift combine

InstCombine uses an IRBuilder that automatically performs
target-dependent constant folding, so explicitly invoking it here
is not necessary.

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -612,14 +612,9 @@ static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
   // We can always evaluate constants shifted.
   if (Constant *C = dyn_cast<Constant>(V)) {
     if (isLeftShift)
-      V = IC.Builder.CreateShl(C, NumBits);
+      return IC.Builder.CreateShl(C, NumBits);
     else
-      V = IC.Builder.CreateLShr(C, NumBits);
-    // If we got a constantexpr back, try to simplify it with TD info.
-    // TODO: This is dubious, IRBuilder<TargetFolder> should already do this.
-    if (auto *C = dyn_cast<Constant>(V))
-      V = ConstantFoldConstant(C, DL, &IC.getTargetLibraryInfo());
-    return V;
+      return IC.Builder.CreateLShr(C, NumBits);
   }
 
   Instruction *I = cast<Instruction>(V);