staging: rtl8188eu: remove the "trigger gpio 0" hal variable

staging: rtl8188eu: remove the "trigger gpio 0" hal variable

The hal variable to trigger gpio 0 seems to be a leftover from debugging
code that was removed. An empty function is called when this variable is
written to.

Remove the empty function and the variable itself. It should be safe to
remove an entry from the hw_variables enum as this enum is used only
within the rtl8188eu driver.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210718173610.894-2-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>