Allow feature gate removal through the API

changelogs/unreleased/zj-feature-gate-remove-http-api.yml

+---
+title: Allow feature gates to be removed through the API
+merge_request:
+author:
+type: added

doc/api/features.md

@@ -86,3 +86,11 @@ Example response:
   ]
 }
 ```
+
+## Delete a feature
+
+Removes a feature gate. Response is equal when the gate exists, or doesn't.
+
+```
+DELETE /features/:name
+```

lib/api/features.rb

@@ -65,6 +65,13 @@ module API
 
         present feature, with: Entities::Feature, current_user: current_user
       end
+
+      desc 'Remove the gate value for the given feature'
+      delete ':name' do
+        Feature.get(params[:name]).remove
+
+        status 204
+      end
     end
   end
 end

spec/requests/api/features_spec.rb

 require 'spec_helper'
 
 describe API::Features do
-  let(:user)  { create(:user) }
-  let(:admin) { create(:admin) }
+  set(:user)  { create(:user) }
+  set(:admin) { create(:admin) }
 
   before do
     Flipper.unregister_groups
@@ -249,4 +249,43 @@ describe API::Features do
       end
     end
   end
+
+  describe 'DELETE /feature/:name' do
+    let(:feature_name) { 'my_feature' }
+
+    context 'when the user has no access' do
+      it 'returns a 401 for anonymous users' do
+        delete api("/features/#{feature_name}")
+
+        expect(response).to have_gitlab_http_status(401)
+      end
+
+      it 'returns a 403 for users' do
+        delete api("/features/#{feature_name}", user)
+
+        expect(response).to have_gitlab_http_status(403)
+      end
+    end
+
+    context 'when the user has access' do
+      it 'returns 204 when the value is not set' do
+        delete api("/features/#{feature_name}", admin)
+
+        expect(response).to have_gitlab_http_status(204)
+      end
+
+      context 'when the gate value was set' do
+        before do
+          Feature.get(feature_name).enable
+        end
+
+        it 'deletes an enabled feature' do
+          delete api("/features/#{feature_name}", admin)
+
+          expect(response).to have_gitlab_http_status(204)
+          expect(Feature.get(feature_name)).not_to be_enabled
+        end
+      end
+    end
+  end
 end