Do we need `Gitlab.config.has_configured_cell?`

The following discussion from !173875 (merged) should be addressed:

• @OmarQunsulGitlab started a discussion: (+3 comments)

  @l.rosa maybe it's not a big deal, but with the change of this line, we will still try to alter the database sequence range if* topology_service is configured, but cell is not configured. Because skip_sequence_alteration? will return false.

  We shouldn't probably do that. Both TS and Cell have to be configured.

  I am sure that we shouldn't configure one of them without the other, but the old line still makes sense as a protection layer.

  Did I miss anything?

Is it because the gRPC call needs the cell name ? Then that's a problem for the TopologyServiceClient, not this rake task. Please create new issue for this.