staging: r8188eu: remove empty trigger gpio code

The hal variable HW_VAR_TRIGGER_GPIO_0 and the rtl8192cu_trigger_gpio_0
function are not used. Remove them.

Acked-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211016113008.27549-2-martin@kaiser.cx


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