monorepo: remove postinstall hook

The docs no longer live in the monorepo so this postinstall
hook is no longer required. It was not caught when removing the
docs because it was designed to never error out.

package.json

@@ -22,7 +22,7 @@
     "lint:specs:check": "npx markdownlint-cli2  \"./specs/**/*.md\"",
     "lint:specs:toc": "npx doctoc '--title=**Table of Contents**' ./specs",
     "preinstall": "npx only-allow pnpm",
-    "postinstall": "patch-package && (test -d docs/op-stack && cd docs/op-stack && npx yarn@1 install && cd ../.. || exit 0)",
+    "postinstall": "patch-package",
     "ready": "pnpm lint && pnpm test",
     "prepare": "husky install",
     "release": "npx nx run-many --target=build --skip-nx-cache && pnpm changeset publish",