[X86] Remove code from combineBitcastvxi1 that was needed to support the...

[X86] Remove code from combineBitcastvxi1 that was needed to support the previous native IR for kunpck intrinsics.

The original autoupgrade for kunpck intrinsics used a bitcasted scalar shift, or, and. This combine would turn this into a concat_vectors. Now the kunpck intrinsics are autoupgraded to a vector shuffle that will become a concat_vectors.

llvm-svn: 323504