Remove mergedConfigurationSelector and legacy schema-style coupling

## Description

Once all consumers have been migrated (#1726, #1727, #1728), the legacy merge system can be deleted.

## Preferred Solution

- Delete `mergedConfigurationSelector` and `mergeConfiguration()`
- Delete `RawConfiguration.schema` (the config-provided schema is defunct)
- Remove the `& VertexPreferencesStorageModel` intersection from `VertexTypeConfig`
- Remove the `& EdgePreferencesStorageModel` intersection from `EdgeTypeConfig`
- Delete any helper functions that only existed to support the 3-way merge (e.g., `patchToRemoveDisplayLabel`)
- Update or remove tests that test the old merge behavior

## Related Issues

- Part of #1677
- Depends on #1726
- Depends on #1727
- Depends on #1728

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Search for mergedConfigurationSelector, mergeConfiguration(), RawConfiguration.schema, the VertexTypeConfig and EdgeTypeConfig intersections, and patchToRemoveDisplayLabel. Review dependent issues #1726, #1727, and #1728 before removing the legacy merge support, then update or remove tests covering the old behavior. Done means the listed legacy APIs, schema coupling, helper functions, and obsolete tests are gone and the test suite passes.

Written by the indexing model from the issue text.