[X86] Remove some uncovered and possibly broken code from combineZext.

This code matches (zext (trunc (setcc_carry))) -> (and (setcc_carry), 1)
but the code never checks what type we're truncating too. An and
mask of 1 would only make sense if the trunc was to MVT::i1, but
we didn't check for that.

I believe this code is a leftover from when i1 was a legal type.

lib/Target/X86/X86ISelLowering.cpp

@@ -43891,18 +43891,6 @@ static SDValue combineZext(SDNode *N, SelectionDAG &DAG,
     }
   }
 
-  if (N0.getOpcode() == ISD::TRUNCATE &&
-      N0.hasOneUse() &&
-      N0.getOperand(0).hasOneUse()) {
-    SDValue N00 = N0.getOperand(0);
-    if (N00.getOpcode() == X86ISD::SETCC_CARRY) {
-      return DAG.getNode(ISD::AND, dl, VT,
-                         DAG.getNode(X86ISD::SETCC_CARRY, dl, VT,
-                                     N00.getOperand(0), N00.getOperand(1)),
-                         DAG.getConstant(1, dl, VT));
-    }
-  }
-
   if (SDValue NewCMov = combineToExtendCMOV(N, DAG))
     return NewCMov;