[X86] Remove SandyBridge CVTSS2SIrm/CVTSD2SIrm overrides

Just use the default WriteCvtSS2I/WriteCvtSD2I folded variants (already used by the VCVTSS2SI/VCVTSD2SI AVX variants).

Confirmed with agner and uops.info - there should be no difference between the SSE/AVX1 variants in folded load latency