Remove the zone-bundle functionality

The sled-agent includes a bunch of code for managing "zone bundles", a tarball of log files and command output run inside a specific, non-global zone on a sled. That was useful during early Omicron development, but is going to be obsoleted by the in-progress work on support bundles. When that's in a reasonable place, we should remove the entire zone-bundling machinery.

Removing the code is mostly fine, but we also have datasets on the M.2s storing the bundles, which is mounted at /pool/int/*/debug/bundle/zone. We'll probably want to add some code in the sled-agent for removing these older datasets entirely.