Staging: delete tty drivers

Delete the drivers/staging/tty drivers as no one has wanted to step up
and maintain and fix them.  This was discussed in commit
4a6514e6d096716fb7bedf238efaaca877e2a7e8 (tty: move obsolete and broken
tty drivers to drivers/staging/tty/)

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>