Remove web_ide_oauth flag and its references

config/feature_flags/development/web_ide_oauth.yml

doc/user/enterprise_user/index.md

doc/user/profile/preferences.md

doc/user/project/web_ide/index.md

ee/spec/lib/ee/web_ide/extensions_marketplace_spec.rb

ee/spec/lib/web_ide/settings/settings_integration_spec.rb

ee/spec/requests/groups_controller_spec.rb

lib/web_ide/default_oauth_application.rb

lib/web_ide/extensions_marketplace.rb

spec/controllers/admin/applications_controller_spec.rb

spec/helpers/ide_helper_spec.rb

spec/lib/web_ide/default_oauth_application_spec.rb

spec/lib/web_ide/extensions_marketplace_spec.rb

spec/requests/ide_controller_spec.rb