Remove legacy keystone.createContext

[timleslie]

See #5025

[changeset-bot]

🦋 Changeset detected

Latest commit: ad5c1af

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 8 packages

Name	Type
@keystone-next/keystone-legacy	Major
@keystone-next/adapter-knex-legacy	Patch
@keystone-next/adapter-mongoose-legacy	Patch
@keystone-next/adapter-prisma-legacy	Patch
@keystone-next/test-utils-legacy	Patch
@keystone-next/benchmarks-legacy	Patch
@keystone-next/keystone	Patch

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