[AArch64] Remove always true Perfect cost check. NFC

Perfect shuffle costs are always encoded less than 4, and shouldn't
really have a cost more than 3, so it makes no sense to check it when
generating shuffles. The perfect shuffle is likely always better than a
tbl too (although that may depend on whether it is in a loop).

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -10204,10 +10204,7 @@ SDValue AArch64TargetLowering::LowerVECTOR_SHUFFLE(SDValue Op,
     unsigned PFTableIndex = PFIndexes[0] * 9 * 9 * 9 + PFIndexes[1] * 9 * 9 +
                             PFIndexes[2] * 9 + PFIndexes[3];
     unsigned PFEntry = PerfectShuffleTable[PFTableIndex];
-    unsigned Cost = (PFEntry >> 30);
-
-    if (Cost <= 4)
-      return GeneratePerfectShuffle(PFEntry, V1, V2, DAG, dl);
+    return GeneratePerfectShuffle(PFEntry, V1, V2, DAG, dl);
   }
   return GenerateTBL(Op, ShuffleMask, DAG);