Stop supporting Google Cloud and Azure as backup strategies

## What does this MR do?

It removes support for Azure and Google Cloud as backup strategies (via Fog).

Motivation behind this decision can be found in !4928, !6713 but basically they require a lot of gems that are unrelated to the backup use-case.

## Are there points in the code the reviewer needs to double check?

Am I missing any other location where we'd use these gems?

See merge request !7739