staging: r8188eu: Remove wrapper rtw_get_time_interval_ms()

This one is never used.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20210805192644.15978-5-Larry.Finger@lwfinger.net


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