Updated instance api endpoints to return empty

• Updated:
- instance api endpoints to return empty, /api/v1/instance /api/v1/instance/peers /api/v1/instance/activity

app/controllers/api/v1/instances_controller.rb

@@ -5,8 +5,6 @@ class Api::V1::InstancesController < Api::BaseController
   skip_before_action :set_cache_headers
 
   def show
-    render_cached_json('api:v1:instances', expires_in: 5.minutes) do
-      ActiveModelSerializers::SerializableResource.new({}, serializer: REST::InstanceSerializer)
-    end
+    render json: {}, content_type: 'application/json'
   end
 end