Do not specify start_pushers in Synapse config

It's unnecessary when `pusher_instances` is populated.

Source: 6acb6d772a

roles/custom/matrix-synapse/defaults/main.yml

@@ -554,11 +554,6 @@ matrix_synapse_workers_pusher_workers_metrics_range_start: 19200
 # Adjusting this value manually is generally not necessary.
 matrix_synapse_federation_pusher_instances: []
 
-# matrix_synapse_start_pushers controls if the main Synapse process should push out notifications or if it should be left to pusher workers (see `matrix_synapse_federation_pusher_instances`).
-# This is enabled if workers are disabled, or if they are enabled, but there are no pusher workers.
-# Adjusting this value manually is generally not necessary.
-matrix_synapse_start_pushers: "{{ not matrix_synapse_workers_enabled or (matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'pusher') | list | length == 0) }}"
-
 # matrix_synapse_workers_federation_sender_workers_count controls the number of federation sender workers to spawn.
 # See https://matrix-org.github.io/synapse/latest/workers.html#synapseappfederation_sender
 matrix_synapse_workers_federation_sender_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['federation_sender_workers_count'] }}"

roles/custom/matrix-synapse/tasks/validate_config.yml

@@ -61,6 +61,7 @@
     - {'old': 'matrix_synapse_workers_frontend_proxy_workers_metrics_range_start', 'new': '<removed in favor of generic workers - see https://github.com/matrix-org/synapse/pull/13645>'}
     - {'old': 'matrix_synapse_ext_s3_storage_provider_path', 'new': 'matrix_synapse_ext_s3_storage_provider_base_path'}
     - {'old': 'matrix_synapse_send_federation', 'new': '<unnecessary - Synapse relies on federation_sender_instances now>'}
+    - {'old': 'matrix_synapse_start_pushers', 'new': '<unnecessary - Synapse relies on pusher_instances now>'}
 
 
 - name: (Deprecation) Catch and report renamed settings in matrix_synapse_configuration_extension_yaml

roles/custom/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -2853,7 +2853,6 @@ federation_sender_instances: {{ matrix_synapse_federation_sender_instances | to_
 {% if matrix_synapse_federation_pusher_instances | length > 0 %}
 pusher_instances: {{ matrix_synapse_federation_pusher_instances | to_json }}
 {% endif %}
-start_pushers: {{ matrix_synapse_start_pushers | to_json }}
 
 # When using workers this should be a map from `worker_name` to the
 # HTTP replication listener of the worker, if configured.