tty_lock: undo the old tty_lock use on the ctty

get_current_tty has its own consistent locking. That means a pile of the
tty lock cases are not needed. As get_current_tty also keeps a reference the
tty object lifetime means we can propogate the lock removal out.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>