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>

diff --cc drivers/tty/tty_port.c
Simple merge

diff --cc include/linux/tty.h
Simple merge