[X86] Remove LowerFCanonicalize and use generic expansion

[RKSimon]

#142105 should provide the generic fallback

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

#142105 should provide the generic fallback

[RKSimon]

@woruyu once #142105 landed (shortly) - would you like to take a look at this?

[woruyu]

@RKSimon Appreciate the ping! I’ll be happy to take a look once it lands!