tty: Remove unused drop() method from tty_port interface

Although originally conceived as a hook for port drivers to know
when a port reference is dropped, no driver uses this method.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_port.c

@@ -484,8 +484,6 @@ int tty_port_close_start(struct tty_port *port,
 
 	if (port->count) {
 		spin_unlock_irqrestore(&port->lock, flags);
-		if (port->ops->drop)
-			port->ops->drop(port);
 		return 0;
 	}
 	set_bit(ASYNCB_CLOSING, &port->flags);
@@ -504,9 +502,7 @@ int tty_port_close_start(struct tty_port *port,
 	/* Flush the ldisc buffering */
 	tty_ldisc_flush(tty);
 
-	/* Don't call port->drop for the last reference. Callers will want
-	   to drop the last active reference in ->shutdown() or the tty
-	   shutdown path */
+	/* Report to caller this is the last port reference */
 	return 1;
 }
 EXPORT_SYMBOL(tty_port_close_start);