Remove the legacy REST API

[amaury1093]

Summary

Remove the legacy REST API for v0.41.

Problem Definition

v0.40 introduced gRPC queries, which should be the preferred way of interacting with the app. For clients still wanting to use REST, all gRPC service methods are annotated to be accessible by REST + HTTP2, using grpc-gateway. Finally, for clients who don't support HTTP2 (e.g. browsers), a grpc-web-proxy is in the works.

All this removes the need of having a separate legacy REST API.

Proposal

• in each module, remove the x/{module}/client/rest folder #9594.
• remove all glue code between simapp/modules and the REST server #9594.

TODO:

• in each module remove the legacy handler and querier #comment.

A clear migration path should also be provided.

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[alexanderbez]

Do we still not need server/api? That's where we serve metrics and the gRPC HTTP gateway, no?

[amaury1093]

True, I updated the initial description.