staging: r8188eu: LED_CTL_START_WPS_BOTTON is not used

None of the callers sets LED_CTL_START_WPS_BOTTON. Remove the define
and related dead code.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211226195556.159471-17-martin@kaiser.cx


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