vfio: remove uneccessary IPC for group fd clear

vfio: remove uneccessary IPC for group fd clear

Clear vfio_group_fd is not necessary to involve any IPC.
Also, current IPC implementation for SOCKET_CLR_GROUP is not
correct. rte_vfio_clear_group on secondary will always fail,
that prevent device be detached correctly on a secondary process.
The patch simply removes all IPC related stuff in
rte_vfio_clear_group.

Fixes: 83a73c5fef66 ("vfio: use generic multi-process channel")
Cc: stable@dpdk.org
Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>