tty: rocket, remove the driver

While the driver is still marked as maintained in MAINTAINERS, Comtrol
does not really care about this ancient driver. They are still
manufacturing serial devices, but those are controlled only by
out-of-tree drivers.

Comtrol didn't answer my pings, so this driver is apparently
unmaintained.  Aside from that, the driver was untouched for years, only
whole-tree changes happened during the past years. The driver needs much
more care, so drop it for now. If someone steps up to reintroduce it,
they need to clean it up first.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-7-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>