staging: r8188eu: remove unused ODM_sleep_us()

Function ODM_sleep_us() is unused, remove it.

Acked-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210911132635.30369-6-straube.linux@gmail.com


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