* combine `JobQueueFederated` and `JobQueueRedis` into a single
`JobQueue` channel.
* Remove duplicate descriptions from file blocks in favour of class
doc blocks. This reduces needless duplication and was often
incorrect or outdated, and helps (ironically) to make the file header
more consistently visually ignorable. Various files in this patch
contained bogus copy-pasta descriptions from unrelated classes,
and re-defined `defgroup JobQueue` many times, showing exactly
how this is defacto ignored and counter-productive to maintain
in two places.
Remove `ingroup` from file blocks in class files as otherwise
the file is indexed twice (e.g. in Doxygen) which makes navigation
on doc.wikimedia.org rather messy for classes in this group.
Ref <https://gerrit.wikimedia.org/r/q/message:ingroup+is:merged>
Change-Id: I926a3aec2bc98fefa1075c4a794c46108579ae3f
