[SelectionDAG] Remove unneeded assert from SelectionDAG::getSignedConstant. NFC (#114336)

This assert is also present inside the APInt constructor after #114539.

Author: topperc

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1773,10 +1773,7 @@ SDValue SelectionDAG::getConstant(const ConstantInt &Val, const SDLoc &DL,
 SDValue SelectionDAG::getSignedConstant(int64_t Val, const SDLoc &DL, EVT VT,
                                         bool isT, bool isO) {
   unsigned Size = VT.getScalarSizeInBits();
-  assert(
-      isIntN(Size, Val) &&
-      "getSignedConstant with a int64_t value that doesn't fit in the type!");
-  return getConstant(APInt(Size, Val, true), DL, VT, isT, isO);
+  return getConstant(APInt(Size, Val, /*isSigned=*/true), DL, VT, isT, isO);
 }
 
 SDValue SelectionDAG::getAllOnesConstant(const SDLoc &DL, EVT VT, bool IsTarget,