It looks like these two classes are also used by Konqueror.

Yes but only because they are hooks for KHTML.

OK, I'll remove the konqueror code first.

Done: https://invent.kde.org/network/konqueror/commit/bfd6ddf5a38f0d21c080a7509d27343ada8aa286

We should keep BrowserInterface after all, it's now used by WebEnginePart too. I'll retitle the task.

In T12225#245842, @dfaure wrote:

Done: https://invent.kde.org/network/konqueror/commit/bfd6ddf5a38f0d21c080a7509d27343ada8aa286

I couldn't readily see where konqueror got to the KHTML part; in retrospect, your commit makes sense.

We should keep BrowserInterface after all, it's now used by WebEnginePart too. I'll retitle the task.

So, konqueror lost some weight/old code, and the task was halved, excellent o/

In T12225#245844, @ahmadsamir wrote:

I couldn't readily see where konqueror got to the KHTML part

Very indirectly: via a KMimeTypeTrader query.

So, konqueror lost some weight/old code, and the task was halved, excellent o/

Yep :)

@dfaure is there anything left to do here, besides adding deprecation markers?

No, that's all that's missing indeed.
https://lxr.kde.org/ident?_i=BrowserHostExtension

https://invent.kde.org/frameworks/kparts/-/merge_requests/15