Revert change to store GraphQL schema in cache

[maxime-rainville]

The change introduced in https://github.com/silverstripe/silverstripe-graphql/pull/534 doesn't seem to be working.

With the beta release so close, it's probably best to revert this.

Acceptance criteria

• https://github.com/silverstripe/silverstripe-graphql/pull/534 has been reverted (just revert the commits)
• Changelog reference have been removed (just revert the commits)
• Other documentation references have been removed (just revert the commits)

PRs

• https://github.com/silverstripe/silverstripe-graphql/pull/548
• https://github.com/silverstripe/developer-docs/pull/324

[GuySartorelli]

@emteknetnz Can you please link all of the PRs?

[emteknetnz]

@GuySartorelli Done

[GuySartorelli]

PRs merged. It's like we never did it in the first place