Remove server scope from Praefect

Praefect's server scope annotation for RPCs is unused unlike storage and repository scopes. Historically the only server scoped RPC was the ServerService.ServerInfo RPC for fetching information about a Gitaly server. Praefect abstracts away the Gitalys and thus intercepts the call and handles it rather than routing to a Gitaly server. The RPC scoping is used for making routing decisions in Praefect. Since Praefect has to intercept any server scoped RPCs, the usage of the scope was replaced by the intercepted option which marks a service as intercepted by Praefect. Since no RPC uses the scope anymore, this MR removes the use of the scope from the few remaining tests and removes the scope from the protobuf definitions.

Closes #3122 (closed)