Move plugin field generation from generated to a factory

addons/api/mirage/factories/host.js

@@ -10,4 +10,9 @@ export default factory.extend({
       'delete',
     ],
   id: (i) => `host-id-${i}`,
+  plugin() {
+    if (this.type === 'plugin') {
+      return this.hostCatalog.plugin;
+    }
+  },
 });

addons/api/mirage/generated/factories/host.js

@@ -13,9 +13,4 @@ export default Factory.extend({
   attributes: () => {
     return { address: internet.ipv6() };
   },
-  plugin: function () {
-    if (this.type === 'plugin') {
-      return this.hostCatalog.plugin;
-    }
-  },
 });