Revert "[AMDGPU][True16] add true16 pattern for cvt_pk_fp32_f8 (#1800… (#191835)
an issue reported with this patch
https://github.com/llvm/llvm-project/issues/191241. Revert for now and
reenable later
This reverts commit e71da01f0f908417723a54cf8829a734a37fa173.