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  - Cleaned up internal APIs by deleting unused exports, imports, and outdated code, enhancing maintainability.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/paragraph/src/index.ts

@@ -2,6 +2,5 @@ export * from './adapters/index.js';
 export * from './commands';
 export * from './paragraph-block.js';
 export * from './paragraph-block-config.js';
-export * from './paragraph-spec.js';
 export * from './turbo/paragraph-layout-handler';
 export * from './turbo/paragraph-painter.worker';

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

@@ -1,34 +0,0 @@
-import { BlockViewExtension, FlavourExtension } from '@blocksuite/std';
-import type { ExtensionType } from '@blocksuite/store';
-import { literal } from 'lit/static-html.js';
-
-import { ParagraphBlockAdapterExtensions } from './adapters/extension.js';
-import { ParagraphBlockConfigExtension } from './paragraph-block-config.js';
-import {
-  ParagraphKeymapExtension,
-  ParagraphTextKeymapExtension,
-} from './paragraph-keymap.js';
-
-const placeholders = {
-  text: "Type '/' for commands",
-  h1: 'Heading 1',
-  h2: 'Heading 2',
-  h3: 'Heading 3',
-  h4: 'Heading 4',
-  h5: 'Heading 5',
-  h6: 'Heading 6',
-  quote: '',
-};
-
-export const ParagraphBlockSpec: ExtensionType[] = [
-  FlavourExtension('affine:paragraph'),
-  BlockViewExtension('affine:paragraph', literal`affine-paragraph`),
-  ParagraphTextKeymapExtension,
-  ParagraphKeymapExtension,
-  ParagraphBlockAdapterExtensions,
-  ParagraphBlockConfigExtension({
-    getPlaceholder: model => {
-      return placeholders[model.props.type];
-    },
-  }),
-].flat();