Kill the DynamicDHGroups feature
In legacy/trac#4548 (moved) we implemented the
DynamicDHGroups feature of prop179 which we ended up never using. It's pretty clear now that we will never use it at all, because we have PTs to do this job.
Since the code is non-trivial, I suggest we kill it completely from the current codebase.
Seems like a good volunteer task too.