tty: remove flags from struct tty_ldisc_ops

The last user was apparently removed by commit a352def2 (tty: Ldisc
revamp) in 2008. So remove the field completely, the only setter
(n_tty_inherit_ops) and also its only possible value
(LDISC_FLAG_DEFINED).

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210914091134.17426-2-jslaby@suse.cz


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