Move responsive headers to cf-core (vendor update)

- Remove `.content_title` and `.content_desc` classes.
- Pull in updated cf-core with responsive headers.
- Replace `.content_title` and `.content_desc` usage with responsive header elements/classes.
- Remove `.u-mb0` class from cf-enhancements since it has been added to cf-core.
- Note: Requires vendor update.

Good point. I made the change based on the idea that these are intended to function as subheaders. But given their structure and the flow of the page, it does make sense to stay with `p` + header class.