[Refactor] Cleanup agent store and actions (#373)

* Cleanup agent store and actions

* Move set/create/update/destroy to helpers

* Update mutation specs

* Add specs for API helper

* Fix edit/delete action visibility

* Add actions specs

* Remove unused API helpers

* Remove duplicates

* Remove duplicates

* Fix duplicate

app/javascript/dashboard/api/endPoints.js

@@ -32,22 +32,6 @@ const endPoints = {
     url: 'api/v1/inboxes.json',
   },
 
-  fetchAgents: {
-    url: 'api/v1/agents.json',
-  },
-
-  addAgent: {
-    url: 'api/v1/agents.json',
-  },
-
-  editAgent(id) {
-    return { url: `api/v1/agents/${id}` };
-  },
-
-  deleteAgent({ id }) {
-    return { url: `api/v1/agents/${id}` };
-  },
-
   createChannel(channel, channelParams) {
     return {
       url: `api/v1/callbacks/register_${channel}_page.json`,