staging: r8188eu: _free_pwrlock is empty

Remove the empty _free_pwrlock function and rtw_free_pwrctrl_priv,
which is just a wrapper around _free_pwrlock.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210913185110.3065-4-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>