Remove outdated Sidekiq alerts

These are:

1. Manually-written.
2. Using metrics (from mtail) that no longer exist.
3. Consequently never going to fire :-)

So we should probably remove them; we already have shard-level apdex alerts that are autogenerated from the metrics catalog.

This part of the file was last touched in !1676 (merged), which said it addressed something missing from !1676 (merged). But it only reformatted the rules with the outdated metrics, and didn't update to use the new metrics 😕