Chore: Remove dead code related to billing (#935)

- remove subscription model
- remove billing-related code

app/javascript/dashboard/api/billing.js

@@ -1,20 +0,0 @@
-/* global axios */
-
-import endPoints from './endPoints';
-
-export default {
-  getSubscription() {
-    const urlData = endPoints('subscriptions').get();
-    const fetchPromise = new Promise((resolve, reject) => {
-      axios
-        .get(urlData.url)
-        .then(response => {
-          resolve(response);
-        })
-        .catch(error => {
-          reject(error);
-        });
-    });
-    return fetchPromise;
-  },
-};

app/javascript/dashboard/api/endPoints.js

@@ -33,14 +33,6 @@ const endPoints = {
     },
     params: { omniauth_token: '' },
   },
-
-  subscriptions: {
-    get() {
-      return {
-        url: '/api/v1/subscriptions',
-      };
-    },
-  },
 };
 
 export default page => {