chore(editor): remove feature flag of embed doc with alias (#12620)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
  - Toolbar actions related to embedding and duplicating documents are now always available without restrictions.

- **Chores**
  - Removed the feature flag controlling embed document alias features for a simpler user experience.

- **Tests**
  - Updated test setup to remove reliance on the deprecated feature flag.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/shared/src/services/feature-flag-service.ts

@@ -19,7 +19,6 @@ export interface BlockSuiteFlags {
   enable_callout: boolean;
   enable_edgeless_scribbled_style: boolean;
   enable_table_virtual_scroll: boolean;
-  enable_embed_doc_with_alias: boolean;
   enable_turbo_renderer: boolean;
   enable_dom_renderer: boolean;
 }
@@ -45,7 +44,6 @@ export class FeatureFlagService extends StoreExtension {
     enable_callout: false,
     enable_edgeless_scribbled_style: false,
     enable_table_virtual_scroll: false,
-    enable_embed_doc_with_alias: false,
     enable_turbo_renderer: false,
     enable_dom_renderer: false,
   });