Change ingress filtering to not decrement the total_measures

[hannosch]

Currently we have an ingress filter limiting the maximum number of observations any single cell/wifi station can get per day.

The tracking of how many items each station can get is based on the total_measures column of the station tables and relies on in/decrementing the column for each day. This means the value doesn't actually reflect the total number of observations anymore.

We should use a separate column for this purpose. After #287 is done, the new_measures column will no longer be used, so we could use it instead and avoid a schema migration.

[hannosch]

Our stats confirmed that the ingress filtering didn't actually catch anything anymore. So removing it was easier than trying to fix it.