[X86] Remove incomplete custom handling of i128 sdivrem/udivrem on Windows.

[X86] Remove incomplete custom handling of i128 sdivrem/udivrem on Windows.

We need to have special handling of i128 div/rem on Windows due
to a weird calling convention needed for the libcall. There was
also some code that made it look like we do the same for sdivrem/udiv,
but the code didn't account for multiple return values of those
functions so couldn't possibly work. I think this code never
triggers because we don't have libcall names defined for those
functions by default so DAGCombine never creates DIVREM nodes.