[X86] Remove MOVDI2SSrm/MOV64toSDrm/MOVSS2DImr/MOVSDto64mr CodeGenOnly instructions.

The isel patterns for these use a bitcast and load/store, but
DAG combine should have canonicalized those away.

For the purposes of the memory folding table these opcodes can be
replaced by the MOVSSrm_alt/MOVSDrm_alt and MOVSSmr/MOVSDmr opcodes.

llvm-svn: 363644