docs+comments: say what changed instead of tagging the tracker item

The prose added by this branch named the tracker item in seventeen
places, which check-issue-refs.sh rejects: a `#N` tag is dead weight for
anyone reading the public mirror, where no issue data exists. Each one
now states the fact it was pointing at — the parent field is gone — so
the sentence stands on its own.

Two of those lines also carried a rustdoc break: `[`write`]` in
topology.rs is ambiguous between the module's own `write` fn and the
`write!` macro, which `-D rustdoc::broken-intra-doc-links` fails. Spelled
`[`write()`]`, per rustdoc's own suggestion.

The host_config.rs rewrite is two lines rather than three so the doc
block stays under check-comment-blocks.sh's 30-line ceiling.

hive-c0re/src/job_queue/exec.rs

@@ -862,8 +862,8 @@ async fn run_deploy_tail(
 /// flake affects — the fan-out set for `MetaUpdate` DAGs. Empty
 /// `inputs` or any input under `hyperhive` → every container;
 /// otherwise just the agents named by `agent-<name>` inputs.
-/// Sorted by name — #4472 removed the parent field the old depth sort
-/// keyed on, and with every agent a root that sort already reduced to
+/// Sorted by name — the parent field the old depth sort keyed on is
+/// gone, and with every agent a root that sort already reduced to
 /// this.
 ///
 /// `inputs` is the caller-supplied flake-input-name list (the dashboard's