Those are the Gmail IMAP folders that show since you setup Gmail as an IMAP account in Mail. You could always setup Gmail again using POP3 instead to get rid of it.
1. Add a new account
2. Fill in name, email address and uncheck the "Set up automatically" checkbox that appears after you fill in yourname@gmail.com
3. You can now fill inn server information etc manually, which includes setting up gmail to use pop:
http://mail.google.com/support/bin/answer.py?hl=en&answer=13275