Remove old relations (#11993)

This is a first PR to remove old relation logic

Next steps:
- remove relationMetadata from cache
- remove relationMetadata table content and structure
- refactor relationDefinition to leverage field.settings instead

packages/twenty-server/src/engine/workspace-manager/workspace-sync-metadata/constants/default-feature-flags.ts

@@ -1,3 +1 @@
-import { FeatureFlagKey } from 'src/engine/core-modules/feature-flag/enums/feature-flag-key.enum';
-
-export const DEFAULT_FEATURE_FLAGS = [FeatureFlagKey.IsNewRelationEnabled];
+export const DEFAULT_FEATURE_FLAGS = [];