[X86][NFC]Remove dead code in IfConversion.cpp

In line 544, if we go in to isFalse, then the Kind could be ICTriangleFalse and isRev must be False, so we never go into the true branch in line 545, better to remove it.

Reviewed By: skan, pengfei

Differential Revision: https://reviews.llvm.org/D157260