summonerd: disable console by default (#4176)

## Describe your changes

The `tokio-console` flag for `summonerd` defaults to `"false"` which
evaluates to `true`. I'm leaving the console subscriber so that we can
activate the unstable flag on a whim, but we should not have it run by
default.

## Checklist before requesting a review

- [x] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

  > Internal CLI change

tools/summonerd/src/main.rs

@@ -87,7 +87,7 @@ operating the orchestration.
 )]
 struct Opt {
     /// Enable Tokio Console support.
-    #[clap(long, default_value = "false")]
+    #[clap(long)]
     tokio_console: bool,
     /// Command to run.
     #[clap(subcommand)]