[AVX512] Remove patterns for (v8f32 (X86vzmovl (insert_subvector undef, (v4f32...

[AVX512] Remove patterns for (v8f32 (X86vzmovl (insert_subvector undef, (v4f32 (scalar_to_vector FR32X:)), (iPTR 0)))) and the same for v4f64.

We don't have this same pattern for AVX2 so I don't believe we should have it for AVX512. We also didn't have it for v16f32.

llvm-svn: 312543