[LegalizeTypes] Remove SoftenFloat handling from ExpandIntRes_LLROUND_LLRINT...

[LegalizeTypes] Remove SoftenFloat handling from ExpandIntRes_LLROUND_LLRINT and remove assert from the strict fp path.

These were both recently added. While the call to GetSoftenedFloat
is a little more optimal, we don't do it in the expand for
FP_TO_SINT/UINT so there's no real reason to do it here. This
avoids a FIXME for strict fp.