Remove unnecessary urls from README (#608)

- Community Q&A site was closed.
- The SDK team no longer posts information to Twitter

Author: Yang-33

README.rst

@@ -326,12 +326,8 @@ Help and media
 --------------
 FAQ: https://developers.line.biz/en/faq/
 
-Community Q&A: https://www.line-community.me/questions
-
 News: https://developers.line.biz/en/news/
 
-Twitter: @LINE_DEV
-
 Versioning
 ----------
 This project respects semantic versioning