drm/amdgpu/sriov: Remove clear vf fw support

PSP clear_vf_fw feature is outdated and has been removed.
Remove the related functions.

Signed-off-by: Victor Zhao <Victor.Zhao@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>