Removed mention of Context and Dataloader in Getting Started with Graphql

[bravely]

As asked in ash-project/ash_hq#122. Ensured locally that it works with everything up to that point.

Contributor checklist

• [ ] Bug fixes include regression tests N/A
• [ ] Features include unit/acceptance tests

[zachdaniel]

🚀 Thank you for your contribution! 🚀