[LegalizeTypes] Remove unnecessary if before calling ReplaceValueWith on the...

[LegalizeTypes] Remove unnecessary if before calling ReplaceValueWith on the chain in SoftenFloatRes_LOAD.

I believe this is a leftover from when fp128 was softened to fp128
on X86-64. In that case type legalization must have been able to
create a load that was the same as N which would make this
replacement fail or assert. Since we no longer do that, this
check should be unneeded.