Remove network checking

Currently Maps uses the GNetworkMonitor from GIO to detect if it has a working network connection, and otherwise shows a "Maps is offline" view, to avoid relying on cached tile data, which might be missing.

Unfortunately this is not always working that reliably for users of certain VPN implementations.

We have discussed removing the network check and assume we have a working network connection for the view (and still show cached tiles, if not) and also make sure things like search can handle not being able to connect correctly.