staging: r8188eu: remove unused function rtw_interface_ps_func()

Remove unused function rtw_interface_ps_func().

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210906190223.11396-8-straube.linux@gmail.com


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