Don't send gitea status update when build is started

This was the source of a flaky test because sometimes hydra-notify was
quick enough to send out `buildStarted` and sometimes it apparently
wasn't which was quickly spottable with `nix build --rebuild`.

Removing that status update doesn't make a difference functionally,
gitea doesn't differentiate between "queued" and "running", so we send
the same status ("pending") out on both events, so we'd even safe one
avoidable request.

flake.nix

@@ -353,10 +353,9 @@
 
                 response = json.loads(data)
 
-                assert len(response) == 3, "Expected exactly three status updates for latest commit (queued, started, finished)!"
+                assert len(response) == 2, "Expected exactly three status updates for latest commit (queued, finished)!"
                 assert response[0]['status'] == "success", "Expected finished status to be success!"
-                assert response[1]['status'] == "pending", "Expected started status to be pending!"
-                assert response[2]['status'] == "pending", "Expected queued status to be pending!"
+                assert response[1]['status'] == "pending", "Expected queued status to be pending!"
 
                 machine.shutdown()
               '';

src/lib/Hydra/Plugin/GiteaStatus.pm

@@ -88,10 +88,6 @@ sub buildQueued {
     common(@_, [], 0);
 }
 
-sub buildStarted {
-    common(@_, [], 1);
-}
-
 sub buildFinished {
     common(@_, 2);
 }