USB: serial: option: drop MeiG Smart defines

Several MeiG Smart modems apparently use the same product id, making the
defines even less useful.

Drop them in favour of using comments consistently to make the id table
slightly less unwieldy.

Cc: stable@vger.kernel.org
Acked-by: Chester A. Unal <chester.a.unal@arinc9.com>
Signed-off-by: Johan Hovold <johan@kernel.org>