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.

I think semantically this should probably remain a `p` element.