tty: drop tty_debug_wait_until_sent()

It's a nop for everyone as TTY_DEBUG_WAIT_UNTIL_SENT is never set.
Provided, we have better debugging/printout mechanisms nowadays, remove
this mechanism.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230810091510.13006-8-jirislaby@kernel.org


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