Chore: remove unused storepb.StoreServer

[pracucci]

What this PR does

We currently define two identical gRPC services: storegatewaypb.StoreGatewayServer and storepb.StoreServer. The former was originally defined in Cortex, while the latter was imported from Thanos. In Mimir, we're using only storegatewaypb.StoreGatewayServer and they're identical because they both import the same data types from storepb.

storepb.StoreServer is only used in tests, but there's no good reason to use it. We can simply use storegatewaypb.StoreGatewayServer in tests too.

In this PR I'm removing storepb.StoreServer.

Is this a breaking change?

No.

storepb.Store_SeriesServer and storegatewaypb.StoreGateway_SeriesServer interfaces are identical. In fact, our gRPC service implementation is StoreGateway.Series(req *storepb.SeriesRequest, srv storegatewaypb.StoreGateway_SeriesServer) which uses the correct one.

Which issue(s) this PR fixes or relates to

N/A

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.

[dimitarvdimitrov]

oh wow so all of our tests were technically running against an API which we don’t serve. Neat. I never realized this. LGTM

[colega]

Is this a breaking change?
No.

It is a breaking change since we're removing the gRPC service. It doesn't affect us because we're not using it, but I think it still should be mentioned in the CHANGELOG at least as "removed unused thanos.Store grpc service from store-gateway".

Edit: oh, now I see, it's not even being served. Then I said nothing.