Removes GCS Adapter from provided adapters

* 💣 removes exposed GCS files adapter

- Should fix problems with GCS
- Throws error that shows the right repo

src/deprecated.js

@@ -0,0 +1,5 @@
+export function useExternal(name, moduleName) {
+  return function() {
+    throw `${name} is not provided by parse-server anymore; please install ${moduleName}`;
+  }
+}