staging: r8188eu: remove OnAtim

Remove the empty OnAtim function. We can set the function pointer in
mlme_sta_tbl to NULL if no action is required for this management frame
subtype.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220421200449.191983-1-martin@kaiser.cx


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