[X86] Remove some patterns that seems to be unreachable.

These patterns mapped (v2f64 (X86vzmovl (v2f64 (scalar_to_vector FR64:$src)))) to a MOVSD and an zeroing XOR. But the complexity of a pattern for (v2f64 (X86vzmovl (v2f64))) that selects MOVQ is artificially and hides this MOVSD pattern.

Weirder still, the SSE version of the pattern was explicitly blocked on SSE41, but yet we had copied it to AVX and AVX512.

llvm-svn: 336556