Add logic to ClientRestResource to decide whether to mount servlets
or not based on whether the current process is a worker.
This is clearer to see what a worker runs than the completely separate /
copy & pasted list of servlets being mounted for workers.
This was the last untyped handler from the HomeServer object. Since
it was being treated as Any (and thus unchecked) it was being used
incorrectly in a few places.
By always using delete_devices and sometimes passing a list
with a single device ID.
Previously these methods had gotten out of sync with each
other and it seems there's little benefit to the single-device
variant.
