staging: r8188eu: remove rtw_mfree_sta_priv_lock function

Remove rtw_mfree_sta_priv_lock function from rtw_sta_mgt.c, as it does
nothing and contains an unused variable.

Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210810235047.177883-5-phil@philpotter.co.uk


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