tty: Remove metag DA TTY and console driver

Now that arch/metag/ has been removed, remove the metag DA TTY and
console driver. It is of no value without the architecture code.

Signed-off-by: James Hogan <jhogan@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-metag@vger.kernel.org