nixos/gitlab: Drop sidekiq PID file

> WARNING: PID file creation will be removed in Sidekiq 6.0, see #4045.
Please use a proper process supervisor to start and manage your
services

Since NixOS uses a proper process supervisor AND does not use the PID
file anywhere, we can just drop it to be upwards compatible and fix that
warning.

nixos/modules/services/misc/gitlab.nix

@@ -704,7 +704,7 @@ in {
         TimeoutSec = "infinity";
         Restart = "on-failure";
         WorkingDirectory = "${cfg.packages.gitlab}/share/gitlab";
-        ExecStart="${cfg.packages.gitlab.rubyEnv}/bin/sidekiq -C \"${cfg.packages.gitlab}/share/gitlab/config/sidekiq_queues.yml\" -e production -P ${cfg.statePath}/tmp/sidekiq.pid";
+        ExecStart="${cfg.packages.gitlab.rubyEnv}/bin/sidekiq -C \"${cfg.packages.gitlab}/share/gitlab/config/sidekiq_queues.yml\" -e production";
       };
     };