To delete the site definitions, go to Manage Sites and just delete the definitions. Site files will still be on your hard drive and will need to be deleted manually. For the recent items, your can clear it by deleting your Dreamweaver preferences I believe, but it's really more trouble than what it's worth. Once you start working on new files the old ones will go away and they should not be of concern.
As for David's tutorial, I will let him speak to that. My thought is that with each new release of DW CC there are nuances that might cause slight differences, but his tutorials are very thorough and should be mostly accurate.
You're likely just using a newer version of the program than David's tutorial was written for. A lot has changed in DW in the last few years and I don't think he's had a chance to go through and update things to match the new screens/menus/options.
You can clean up your sites by...
1. Go to Site > Manage Sites
2. Click the one(s) you want to get rid of to highlight them
3. Hit the - button in the bottom left
4. Click Yes to delete
That will only remove the Site Definition from DW. If you want to also remove the site files from your computer, you'll need to browse to the folder you set up when creating the site and drop it in your Recycling Bin/Trash
Many thanks Jon Fritz ii.
Ben has answered your question regarding deleting site definitions and related files.
With regard to your problem with my Responsive Design with Bootstrap and Dreamweaver CC course on lynda.com, it was recorded using a prerelease version of Dreamweaver CC 2015.1, so there should be no inconsistencies as long as you have installed the most recent version of Dreamweaver. I suspect that your problem with the chevron icon is due to a typing error. If you check the video at about 04:10, the text I have typed is <span class="glyphicon. What you have typed here is <span class="glyphon. That would explain the lack of code hints and why the chevron wasn't displayed.
I'm quite happy to answer questions about my course in this forum, but I won't necessarily see them. If you're a subscriber to lynda.com, you can get help with problems by using the form on the following page: Contact lynda.com through phone or email. Select Customer Service and Technical Support from the drop-down menu, and fill in the form that appears. If you go to that page directly from the video that gave you problems, the form will automatically be filled in with some useful details. If the technical support people at lynda.com can't answer your question, they email it to me directly. In most cases, I reply within 12 hours.
Thanks David. I have bookmarked the Lynda contact page. I subscribe to to Adobe CC so thanks to Cloud membership my programmes are always up to date. My new rule - check copy before shouting!