refactor(editor): cleanup dead code (#12281)

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

- **Refactor**
  - Streamlined and consolidated block and inline extension exports by removing multiple block-spec and inline extension arrays from public APIs.
  - Reduced exported constants, types, and utility functions related to various block and embed features.
  - Simplified the codebase by removing deprecated type guards, adapter extensions, and redundant extension groupings.
- **Chores**
  - Cleaned up internal APIs by deleting unused exports, imports, and outdated code, enhancing maintainability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/blocks/divider/src/divider-spec.ts

@@ -1,10 +0,0 @@
-import { BlockViewExtension } from '@blocksuite/std';
-import type { ExtensionType } from '@blocksuite/store';
-import { literal } from 'lit/static-html.js';
-
-import { DividerBlockAdapterExtensions } from './adapters/extension.js';
-
-export const DividerBlockSpec: ExtensionType[] = [
-  BlockViewExtension('affine:divider', literal`affine-divider`),
-  DividerBlockAdapterExtensions,
-].flat();

blocksuite/affine/blocks/divider/src/index.ts

@@ -1,3 +1,2 @@
 export * from './adapters';
 export * from './divider-block';
-export * from './divider-spec';