[X86] Remove isel patterns that include a vselect/X86selects and a strict FP node.

A vselect+strictfp node is not equivalent to a masked operation.
The exceptions of the strictfp node are not masked by a vselect
after it so we can't match it to a masked operation.

We already had a hack in IsLegalToFold to prevent these patterns from
matching. This patch removes that hack and removes the patterns.