Remove search_index_all_projects FF

...g/feature_flags/development/search_index_all_projects.yml

doc/integration/advanced_search/elasticsearch.md

ee/app/models/concerns/elastic/projects_search.rb

ee/app/models/elasticsearch_indexed_project.rb

ee/app/workers/elastic/project_transfer_worker.rb

ee/app/workers/elastic_commit_indexer_worker.rb

ee/app/workers/elastic_namespace_indexer_worker.rb

ee/app/workers/elastic_wiki_indexer_worker.rb

ee/spec/models/concerns/elastic/project_spec.rb

ee/spec/models/elasticsearch_indexed_project_spec.rb

ee/spec/services/search/rake_task_executor_service_spec.rb

ee/spec/workers/elastic/project_transfer_worker_spec.rb

ee/spec/workers/elastic_commit_indexer_worker_spec.rb

ee/spec/workers/elastic_namespace_indexer_worker_spec.rb

ee/spec/workers/elastic_wiki_indexer_worker_spec.rb