Removing xsd-fu &linking to new BF version instead

The new BF page on xsd-fu is now live, this PR removes the out of date version from the Model & Formats docs and links developers to the BF page instead.

**Develop-only**
This only affects the formats docs, the dev_4_4 version of which is now essentially legacy and the new file doesn't exist on BF dev_4_4.