Removed API endpoint and specs

.codeclimate.yml

.rubocop_todo.yml

app/models/application_setting.rb

app/models/concerns/project_features_compatibility.rb

changelogs/unreleased/fj-36819-remove-v3-api.yml

doc/api/README.md

doc/api/applications.md

doc/api/environments.md

doc/api/projects.md

doc/api/v3_to_v4.md

doc/integration/shibboleth.md

lib/api/api.rb

lib/api/v3/award_emoji.rb

lib/api/v3/boards.rb

lib/api/v3/branches.rb

lib/api/v3/broadcast_messages.rb

lib/api/v3/builds.rb

lib/api/v3/commits.rb

lib/api/v3/deploy_keys.rb

lib/api/v3/deployments.rb