staging: r8188eu: remove unused function rtw_add_bcn_ie()

Function rtw_add_bcn_ie() is not used anywhere, remove it.

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210819112200.32030-1-straube.linux@gmail.com


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