Revert "- Expand support of MANY_TO_MANY relations to remove join table entries to models that are no longer referenced by owner model. Does not delete the actual models, only join table links."

This reverts commit 4f52651aab7fc8887cb5b75013c307b69b4e938e.
- Expand support of MANY_TO_MANY relations to remove join table entries to models that are no longer referenced by owner model. Does not delete the actual models, only join table links.
- Implement unlink for MANY_TO_MANY relations.

- Re-uploading the same changes as the last commit but fixing the whitespace bug making it impossible to see actual changes.
- Changed the "delete" part of the code to only do *ONE* query. Copied from official pull request https://github.com/yiiext/with-related-behavior/pull/32