Review RemoteSettings for ESR78

We should revisit #31740 (closed) for ESR78. In a first inspection I could see requests to url-classifier-skip-urls, which the current patch should have removed.

We could also use the opportunity to simplify the patch a bit, for example trying to make all the changes in a single place (e.g. something like a blacklist of bucket/collection somewhere in the RemoteSettings client code).