mpam/resctrl: Clean up resctrl_group_rmdir_[ctrl/mon]()

hulk inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I9NZ3E



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resctrl_group_rm_ctrl() is only called in resctrl_group_rmdir_ctrl(), so
merge resctrl_group_rm_ctrl() and resctrl_group_rmdir_ctrl() for the
following fix patch. Also do the same on resctrl_group_rm_mon() and
resctrl_group_rmdir_mon().

No functional change.

Signed-off-by: Yu Liao <liaoyu15@huawei.com>