Remove leftover mentions to fixtures

Author: Arkham

.changeset/config.json

@@ -8,7 +8,6 @@
     "@shopify/app",
     "@shopify/create-app",
     "@shopify/cli-kit",
-    "@shopify/fixtures-app",
     "@shopify/theme",
     "@shopify/ui-extensions-dev-console-app",
     "@shopify/plugin-ngrok",

.changeset/pre.json

@@ -2,7 +2,6 @@
   "mode": "pre",
   "tag": "pre",
   "initialVersions": {
-    "@shopify/fixtures-app": "3.44.0",
     "shopify-app-template-node": "0.1.0",
     "starter-react-frontend-app": "0.1.0",
     "@shopify/app": "3.44.0",

.nxignore

@@ -1,3 +1,2 @@
 **/templates/**
 docs/**
-fixtures/**