Remove the circuit breaker API

The circuit breaker itself was removed in 11.5, this removes the
corresponding API endpoints which returned empty data since then.

changelogs/unreleased/chore-remove-circuit-breaker-api.yml

+---
+title: Remove the circuit breaker API
+merge_request: 28669
+author:
+type: removed

doc/api/repository_storage_health.md

-# Circuitbreaker API
-
-NOTE: **Deprecated:**
-Support of the circuit breaker is removed, as Gitaly can be configured to 
-to work without NFS and [communicate solely over HTTP](../administration/gitaly/index.md).

lib/api/api.rb

@@ -98,7 +98,6 @@ module API
     mount ::API::Boards
     mount ::API::Branches
     mount ::API::BroadcastMessages
-    mount ::API::CircuitBreakers
     mount ::API::Commits
     mount ::API::CommitStatuses
     mount ::API::ContainerRegistry

lib/api/circuit_breakers.rb

-# frozen_string_literal: true
-
-module API
-  class CircuitBreakers < Grape::API
-    before { authenticated_as_admin! }
-
-    resource :circuit_breakers do
-      params do
-        requires :type,
-                 type: String,
-                 desc: "The type of circuitbreaker",
-                 values: ['repository_storage']
-      end
-      resource ':type' do
-        namespace '', requirements: { type: 'repository_storage' } do
-          desc 'Get all git storages' do
-            detail 'This feature was introduced in GitLab 9.5'
-          end
-          get do
-            present []
-          end
-
-          desc 'Get all failing git storages' do
-            detail 'This feature was introduced in GitLab 9.5'
-          end
-          get 'failing' do
-            present []
-          end
-
-          desc 'Reset all storage failures and open circuitbreaker' do
-            detail 'This feature was introduced in GitLab 9.5'
-          end
-          delete do
-          end
-        end
-      end
-    end
-  end
-end

spec/requests/api/circuit_breakers_spec.rb

-require 'spec_helper'
-
-describe API::CircuitBreakers do
-  set(:user) { create(:user) }
-  set(:admin) { create(:admin) }
-
-  describe 'GET circuit_breakers/repository_storage' do
-    it 'returns a 401 for anonymous users' do
-      get api('/circuit_breakers/repository_storage')
-
-      expect(response).to have_gitlab_http_status(401)
-    end
-
-    it 'returns a 403 for users' do
-      get api('/circuit_breakers/repository_storage', user)
-
-      expect(response).to have_gitlab_http_status(403)
-    end
-
-    it 'returns an Array of storages' do
-      get api('/circuit_breakers/repository_storage', admin)
-
-      expect(response).to have_gitlab_http_status(200)
-      expect(json_response).to be_kind_of(Array)
-      expect(json_response).to be_empty
-    end
-
-    describe 'GET circuit_breakers/repository_storage/failing' do
-      it 'returns an array of failing storages' do
-        get api('/circuit_breakers/repository_storage/failing', admin)
-
-        expect(response).to have_gitlab_http_status(200)
-        expect(json_response).to be_kind_of(Array)
-        expect(json_response).to be_empty
-      end
-    end
-  end
-
-  describe 'DELETE circuit_breakers/repository_storage' do
-    it 'clears all circuit_breakers' do
-      delete api('/circuit_breakers/repository_storage', admin)
-
-      expect(response).to have_gitlab_http_status(204)
-    end
-  end
-end