add migration to remove the old tables, and some cleanup

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/khaki-adults-own.md

@@ -0,0 +1,56 @@
+---
+'@backstage/plugin-catalog-backend': minor
+---
+
+**BREAKING CHANGE**: Removed all remnants of the old catalog engine
+implementation.
+
+The old implementation has been deprecated for over half a year. To ensure that
+you are not using the old implementation, check that your
+`packages/backend/src/plugins/catalog.ts` creates the catalog builder using
+`CatalogBuilder.create`. If you instead call `new CatalogBuilder`, you are on
+the old implementation and will experience breakage if you upgrade to this
+version. If you are still on the old version, see [the relevant change log
+entry](https://github.com/backstage/backstage/blob/master/plugins/catalog-backend/CHANGELOG.md#patch-changes-27)
+for migration instructions.
+
+The following classes and interfaces have been removed:
+
+- The `CatalogBuilder` constructor (see above; use `CatalogBuilder.create`
+  instead)
+- `AddLocationResult`
+- `CommonDatabase`
+- `CreateDatabaseOptions`
+- `createNextRouter` (use `createRouter` instead - or preferably, use the
+  `router` field returned for you by `catalogBuilder.build()`)
+- `Database`
+- `DatabaseEntitiesCatalog` (use `EntitiesCatalog` instead)
+- `DatabaseLocationsCatalog` (use `LocationService` instead)
+- `DatabaseLocationUpdateLogEvent`
+- `DatabaseLocationUpdateLogStatus`
+- `DatabaseManager`
+- `DbEntitiesRequest`
+- `DbEntitiesResponse`
+- `DbEntityRequest`
+- `DbEntityResponse`
+- `DbLocationsRow`
+- `DbLocationsRowWithStatus`
+- `DbPageInfo`
+- `HigherOrderOperation`
+- `HigherOrderOperations`
+- `LocationReader`
+- `LocationReaders`
+- `LocationResponse`
+- `LocationsCatalog`
+- `LocationUpdateLogEvent`
+- `LocationUpdateStatus`
+- `NextCatalogBuilder` (use `CatalogBuilder.create` instead)
+- `NextRouterOptions` (use `RouterOptions` instead)
+- `ReadLocationEntity`
+- `ReadLocationError`
+- `ReadLocationResult`
+- `Transaction`
+
+The `RouterOptions` interface has been un-deprecated, and has instead found use
+for passing into `createRouter`. Its shape has been significantly changed to
+accommodate the new router.