Fall back to GeoIP for incomplete search requests, closes #343.

Historically we had rather strict requirements for well-formed requests, lowering these requirements over time. As one of the last changes we allowed the exact payload of `{}` as a valid request to mean "give me a GeoIP result". As the bug says, Firefox doesn't actually send an empty mapping, but instead `{"wifiAccessPoints": []}`. Instead of special casing this again, I've just dropped the "you need to send one cell or wifi" validator, which means most malformed or empty requests will return GeoIP results now.

The change in ichnaea/service/submit/views.py / submit_validator is a drive-by fix, removing a block that didn't actually do anything.

@jaredkerim r?