staging: r8188eu: remove unused action handler prototypes

For some action categories, we removed the handler function, but we forgot
the prototypes. Remove them as well.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220502200652.143665-4-martin@kaiser.cx


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