staging: r8188eu: LED_CTL_POWER_ON is not used

The LED_CTL_POWER_ON mode is not used by this driver.
Remove the define and related dead code.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211226195556.159471-16-martin@kaiser.cx


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