[X86] Remove combine that turns X86ISD::LSUB into X86ISD::LADD. Update...

[X86] Remove combine that turns X86ISD::LSUB into X86ISD::LADD. Update patterns that depended on this.

If the carry flag is being used, this transformation isn't safe.

This does prevent some test cases from using DEC now, but I'll try to look into that separately.

Fixes PR35068.

llvm-svn: 316860