Trying to do hooks generically is way too complicated and unreliable and

confusing, particularly trying to automatically figure out what target
hooks should be using. So simplify it:

- drop before hooks entirely, they don't seem to be very useful;

- commands with special requirements now fire their own after hook (for
  example, if they change session or window, or if they have -t and -s
  and need to choose which one the hook uses as current target);

- commands with no special requirements can have the CMD_AFTERHOOK flag
  added and they will use the -t state.

At the moment new-session, new-window, split-window fire their own hook,
and display-message uses the flag. The remaining commands still need to
be looked at.

cmd-swap-window.c

@@ -84,12 +84,5 @@ cmd_swap_window_exec(struct cmd *self, struct cmd_q *cmdq)
 	}
 	recalculate_sizes();
 
-	cmd_find_clear_state(&cmdq->current, NULL, 0);
-	cmdq->current.s = dst;
-	cmdq->current.wl = wl_dst;
-	cmdq->current.w = wl_dst->window;
-	cmdq->current.wp = cmdq->state.sflag.wp;
-	cmd_find_log_state(__func__, &cmdq->current);
-
 	return (CMD_RETURN_NORMAL);
 }