selftests/resctrl: Remove mum_resctrlfs from struct resctrl_val_param

Resctrl FS mount/umount are now cleanly paired leaving .mum_resctrlfs
in the struct resctrl_val_param unused.

Remove .mum_resctrlfs from struct resctrl_val_param.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan (Fujitsu) <tan.shaopeng@fujitsu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>