Upgrade Synapse (v1.66.0 -> 1.67.0) and remove frontend_proxy workers

`frontend_proxy` workers have been superseded by `generic_worker` workers.
Related to https://github.com/matrix-org/synapse/pull/13645

roles/matrix-synapse/vars/workers.yml

@@ -55,10 +55,12 @@ matrix_synapse_workers_generic_worker_endpoints:
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/search$
 
   # Encryption requests
+  # Note that ^/_matrix/client/(r0|v3|unstable)/keys/upload/ requires `worker_main_http_uri`
   - ^/_matrix/client/(r0|v3|unstable)/keys/query$
   - ^/_matrix/client/(r0|v3|unstable)/keys/changes$
   - ^/_matrix/client/(r0|v3|unstable)/keys/claim$
   - ^/_matrix/client/(r0|v3|unstable)/room_keys/
+  - ^/_matrix/client/(r0|v3|unstable)/keys/upload/
 
   # Registration/login requests
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/login$
@@ -172,7 +174,6 @@ matrix_synapse_workers_generic_worker_endpoints:
 
   # Additionally, the writing of specific streams (such as events) can be moved off
   # of the main process to a particular worker.
-  # (This is only supported with Redis-based replication.)
 
   # To enable this, the worker must have a HTTP replication listener configured,
   # have a `worker_name` and be listed in the `instance_map` config. The same worker
@@ -432,35 +433,9 @@ matrix_synapse_workers_user_dir_endpoints:
   # If `update_user_directory` is set to `false`, and this worker is not running,
   # the above endpoint may give outdated results.
 
-matrix_synapse_workers_frontend_proxy_endpoints:
-  # Proxies some frequently-requested client endpoints to add caching and remove
-  # load from the main synapse. It can handle REST endpoints matching the following
-  # regular expressions:
-
-  - ^/_matrix/client/(r0|v3|unstable)/keys/upload
-
-  # If `use_presence` is False in the homeserver config, it can also handle REST
-  # endpoints matching the following regular expressions:
-
-  # FIXME: ADDITIONAL CONDITIONS REQUIRED: to be enabled manually
-  # ^/_matrix/client/(api/v1|r0|v3|unstable)/presence/[^/]+/status
-
-  # This "stub" presence handler will pass through `GET` request but make the
-  # `PUT` effectively a no-op.
-
-  # It will proxy any requests it cannot handle to the main synapse instance. It
-  # must therefore be configured with the location of the main instance, via
-  # the `worker_main_http_uri` setting in the `frontend_proxy` worker configuration
-  # file. For example:
-
-  # ```yaml
-  # worker_main_http_uri: http://127.0.0.1:8008
-  # ```
-
 matrix_synapse_workers_avail_list:
   - appservice
   - federation_sender
-  - frontend_proxy
   - generic_worker
   - media_repository
   - pusher