synapse workers: supply systemd with actual worker PIDs (requires jq)

also, worker.yaml.j2:
  - hone worker_name
  - remove worker_pid_file entry (would only be used if worker_daemonize
    set to true; also, synapse only knows about the container namespace
    and thus can not provide the required host-view PID)

roles/matrix-synapse/tasks/workers/setup_uninstall.yml

@@ -36,3 +36,8 @@
 - name: Ensure systemd noticed removal of worker service units
   service:
     daemon_reload: yes
+
+- name: Ensure matrix-synapse-worker-write-pid script is removed
+  file:
+    path: "{{ matrix_local_bin_path }}/matrix-synapse-worker-write-pid"
+    state: absent