staging: r8188eu: remove unused function prototype

Remove the prototype for rtl8188eu_recv_hdl. This function does not exist
in the r8188eu driver.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220315205041.2714168-4-martin@kaiser.cx


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