remove optional adapters from default dependencies

[championswimmer]

In extension of the discussion here #761
We should move out adapters like the GCS adapter or S3 adapter from parse's default dependencies.

If I want to use a simple fs backed storage, I have no use downloading those adapters from npm.

It can simply be mentioned on the Wiki https://github.com/ParsePlatform/parse-server/wiki/Configuring-File-Adapters#configuring-s3adapter that you need to add the adapter to your package.json.

[flovilmart]

there's a PR for that already #1339