Remove legacy list adapter methods

[timleslie]

These methods were all either unused or barely used, and no longer things we want to explicitly expose in our APIs.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6f0d263

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/adapter-prisma-legacy	Major
@keystone-next/fields-legacy	Patch
@keystone-next/keystone-legacy	Patch
@keystone-next/fields-auto-increment-legacy	Patch
@keystone-next/test-utils-legacy	Patch
@keystone-next/fields-document	Patch
@keystone-next/keystone	Patch

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