Cleaned CommentThread model
Cleaned CommentThread model

- Removed dead code
- Replaced unnecessary double quotes with single quotes
- Reformatted one-line methods

edx/cs_comments_service,Stanford-Online/cs_comments_service,edx-solutions/cs_comments_service,EDUlib/cs_comments_service,edx/cs_comments_service,edx-solutions/cs_comments_service,Stanford-Online/cs_comments_service,EDUlib/cs_comments_service,edx-solutions/cs_comments_service,EDUlib/cs_comments_service,Stanford-Online/cs_comments_service,edx/cs_comments_service