Revert "tty: add the option to have a tty reject a new ldisc"

This reverts commit 3c6332f3 which is
commit 6bd23e0c upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ia8d68d62f97da2536404bfb439f2db596033260f
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>