Documentation/serial: Delete obsolete driver documentation

These serial drivers were removed in kernel v3.1, so we can drop their
documentation files and references to their magic numbers and
parameters.

There are still references to these old drivers in
Documentation/devices.txt but I'm afraid they can't be removed.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Rob Landley <rob@landley.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>