Remove IS_WORKSPACE_MIGRATION_V2_ENABLED feature flag (#16280)

# Introduction
closes https://github.com/twentyhq/core-team-issues/issues/1911

packages/twenty-server/src/engine/workspace-manager/dev-seeder/core/utils/seed-feature-flags.util.ts

@@ -1,7 +1,6 @@
 import { type QueryRunner } from 'typeorm';
 
 import { FeatureFlagKey } from 'src/engine/core-modules/feature-flag/enums/feature-flag-key.enum';
-import { SEED_APPLE_WORKSPACE_ID } from 'src/engine/workspace-manager/dev-seeder/core/constants/seeder-workspaces.constant';
 
 const tableName = 'featureFlag';
 
@@ -57,11 +56,6 @@ export const seedFeatureFlags = async ({
         workspaceId: workspaceId,
         value: true,
       },
-      {
-        key: FeatureFlagKey.IS_WORKSPACE_MIGRATION_V2_ENABLED,
-        workspaceId: workspaceId,
-        value: workspaceId === SEED_APPLE_WORKSPACE_ID,
-      },
       {
         key: FeatureFlagKey.IS_PAGE_LAYOUT_ENABLED,
         workspaceId: workspaceId,