Remove dead Elasticsearch indexing locking code

The code paths that used to use these locks have been long removed so we
can safely remove them. Additionally these are superceded by better
de-duplication mechanisms including sidekiq queue de-duplication for
`ElasticCommitIndexerWorker`, redis sorted sets for other indexing jobs
and finally we added a lock inside of `ElasticCommitIndexerWorker`
recently to avoid a related problem that these locks didn't even cover
anyway https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35842 .

doc/integration/elasticsearch.md

@@ -566,12 +566,6 @@ Here are some common pitfalls and how to overcome them:
 
   You can run `sudo gitlab-rake gitlab:elastic:projects_not_indexed` to display projects that aren't indexed.
 
-- **No new data is added to the Elasticsearch index when I push code**
-
-  When performing the initial indexing of blobs, we lock all projects until the project finishes indexing. It could
-  happen that an error during the process causes one or multiple projects to remain locked. In order to unlock them,
-  run the `gitlab:elastic:clear_locked_projects` Rake task.
-
 - **"Can't specify parent if no parent field has been configured"**
 
   If you enabled Elasticsearch before GitLab 8.12 and have not rebuilt indexes you will get

ee/app/services/ee/git/branch_push_service.rb

@@ -34,12 +34,8 @@ module EE
 
       def should_index_commits?
         return false unless default_branch?
-        return false unless project.use_elasticsearch?
 
-        # Check that we're not already indexing this project
-        ::Gitlab::Redis::SharedState.with do |redis|
-          !redis.sismember(:elastic_projects_indexing, project.id)
-        end
+        project.use_elasticsearch?
       end
     end
   end

ee/lib/tasks/gitlab/elastic.rake

@@ -46,13 +46,6 @@ namespace :gitlab do
       puts "Indexing is %.2f%% complete (%d/%d projects)" % [percent, indexed, projects]
     end
 
-    desc 'GitLab | Elasticsearch | Unlock repositories for indexing in case something gets stuck'
-    task clear_locked_projects: :environment do
-      Gitlab::Redis::SharedState.with { |redis| redis.del(:elastic_projects_indexing) }
-
-      puts 'Cleared all locked projects. Incremental indexing should work now.'
-    end
-
     desc "GitLab | Elasticsearch | Index all snippets"
     task index_snippets: :environment do
       logger = Logger.new(STDOUT)
@@ -127,7 +120,6 @@ namespace :gitlab do
 
       relation.all.in_batches(start: ENV['ID_FROM'], finish: ENV['ID_TO']) do |relation| # rubocop: disable Cop/InBatches
         ids = relation.reorder(:id).pluck(:id)
-        Gitlab::Redis::SharedState.with { |redis| redis.sadd(:elastic_projects_indexing, ids) }
         yield ids
       end
     end

ee/spec/services/ee/git/branch_push_service_spec.rb

@@ -42,18 +42,6 @@ RSpec.describe Git::BranchPushService do
         stub_ee_application_setting(elasticsearch_indexing?: true)
       end
 
-      context 'when the project is locked by elastic.rake', :clean_gitlab_redis_shared_state do
-        before do
-          Gitlab::Redis::SharedState.with { |redis| redis.sadd(:elastic_projects_indexing, project.id) }
-        end
-
-        it 'does not run ElasticCommitIndexerWorker' do
-          expect(ElasticCommitIndexerWorker).not_to receive(:perform_async)
-
-          subject.execute
-        end
-      end
-
       it 'runs ElasticCommitIndexerWorker' do
         expect(ElasticCommitIndexerWorker).to receive(:perform_async).with(project.id)