Fix duplicate entry in SUMMARY.md

Remove duplicate reference to doc-comment.md that was causing mdbook build to fail.
The file was referenced twice:
- Under "Code comment" section (kept)
- Under "Viết Docs" section (removed)

This resolves the build error:
"Duplicate file in SUMMARY.md: ./basic/code-comment/doc-comment.md"

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: claude

src/SUMMARY.md

@@ -120,7 +120,6 @@
 
 - [Viết Docs](./basic/rustdoc/README.md)
 
-  - [Doc comments](./basic/code-comment/doc-comment.md)
   - [Sử dụng README.md làm crate document](./basic/rustdoc/doc-README.md)