API: Remove XML tag highlighting from non-XML formats

API: Remove XML tag highlighting from non-XML formats

Since 926afc65c316, the transformation assumes < and > occur in pairs.
This assumption is invalid for formats such as JSON.

Implementing proper JSON syntax highlighting falls outside the scope
of this workaround and is left for separate changes, likely including
the addition of a hook. That is part of the API roadmap RfC.

https://www.mediawiki.org/wiki/Requests_for_comment/API_roadmap#Changes_to_pretty-printed_HTML_formats

Bug: 65403
Change-Id: Iff8d444c82f7efd2bd1c9f703defc4f0984e8211