dirmgr: do not pass fallbacks to the CircMgr.

This is the final step in allowing the CircMgr to use the GuardMgr's
view of the fallbacks.

Compilation is restored and tests pass.

crates/tor-dirmgr/src/bootstrap.rs

@@ -59,14 +59,9 @@ async fn fetch_single<R: Runtime>(
     }
     let circmgr = dirmgr.circmgr()?;
     let cur_netdir = dirmgr.opt_netdir();
-    let config = dirmgr.config.get();
-    let fbs;
     let dirinfo = match cur_netdir {
         Some(ref netdir) => netdir.as_ref().into(),
-        None => {
-            fbs = config.fallbacks().iter().collect::<Vec<_>>();
-            fbs[..].into()
-        }
+        None => tor_circmgr::DirInfo::Nothing,
     };
     let outcome =
         tor_dirclient::get_resource(request.as_requestable(), dirinfo, &dirmgr.runtime, circmgr)