You're right, it's better if this lands first.
With 196 changed files, I have to merge very often anyway.

We need to check if any published extension uses utils/CollectionUtils. Otherwise this extension would be broken.

@ingorichter I thought about that already. I thought there was an extension by someone on the core team that helped figuring that out, but I can't seem to find it anymore.

EDIT: I think I found it. https://github.com/dangoor/BracketsExtensionGrabber Will comment again with extension report.

EDIT 2: Initial pass of all the uploaded extensions (as gathered by the aforementioned tool) reports no usage of utils/CollectionsUtils, only small usage of StringUtils.htmlEscape() in four extensions:

https://github.com/peterflynn/eval-in-browser
https://github.com/tomsdev/brackets-typescript-code-intel
https://github.com/iwehrman/brackets-simple-js-code-hints
https://github.com/adobe/brackets-edge-web-fonts (PR to fix this at adobe/brackets-edge-web-fonts#174)

Will have results of a more extensive search a little later.

EDIT 3: Through scan complete, no usage of utils/CollectionsUtils found.

Sounds good. If none of the Extensions is using utils/CollectionUtils, then we can assume that this is safe to get rid off.
It would be a good idea to file an issue with all 4 extension authors and tell them that StringUtils.htmlEscape has been removed after a long deprecation phase. This will put the ball in their court and we can move on. Sounds good?

Done. All issues at extension repos have been filed.

Just updated with master, this is ready to be merged again.

Looks good to me. All tests pass on OSX.