[X86] Remove EFLAGS from live-in lists in X86FlagsCopyLowering.

When EFLAGS is no longer live into a basic block, remove it from the live-in
list.

Fixes https://bugs.llvm.org/show_bug.cgi?id=44462.

Review: Craig Topper

Differential Revision: https://reviews.llvm.org/D71375