Prevent double-quotes around default room version

Using `|to_json` on a string is expected to correctly wrap it in quotes (e.g. `"4"`).
Wrapping it explicitly in double-quotes results in undesirable double-quoting (`""4""`).

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

@@ -82,7 +82,7 @@ use_presence: {{ matrix_synapse_use_presence|to_json }}
 # For example, for room version 1, default_room_version should be set
 # to "1".
 #
-default_room_version: "{{ matrix_synapse_default_room_version|to_json }}"
+default_room_version: {{ matrix_synapse_default_room_version|to_json }}
 
 # The GC threshold parameters to pass to `gc.set_threshold`, if defined
 #