chore(monorepo-gerrit): Remove 'owners-autoassign' plugin

This plugin just blindly assigns everyone and, as q3k has already
pointed out, just isn't particularly useful.

We might want to roll our own, for example:

19: 40:41 <+Remosi> I want the virtual owner thing, we could call it
 Gerrit Workgroup Synthesizer Queuing, or gwsq for short.
Change-Id: Ib12a921ae4047ac6a734035dd0900c8964fb12d8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/350
Reviewed-by: riking <rikingcoding@gmail.com>

ops/nixos/monorepo-gerrit.nix

@@ -19,7 +19,6 @@ in {
 
     plugins = with config.depot.third_party.gerrit_plugins; [
       owners
-      owners-autoassign
     ];
 
     package = config.depot.third_party.gerrit;