Add MQTT removal migration and fix tests + docs

frontend/src/test/settingsModal.test.tsx

@@ -51,21 +51,6 @@ const baseSettings: AppSettings = {
   preferences_migrated: false,
   advert_interval: 0,
   last_advert_time: 0,
-  bots: [],
-  mqtt_broker_host: '',
-  mqtt_broker_port: 1883,
-  mqtt_username: '',
-  mqtt_password: '',
-  mqtt_use_tls: false,
-  mqtt_tls_insecure: false,
-  mqtt_topic_prefix: 'meshcore',
-  mqtt_publish_messages: false,
-  mqtt_publish_raw_packets: false,
-  community_mqtt_enabled: false,
-  community_mqtt_iata: '',
-  community_mqtt_broker_host: 'mqtt-us-v1.letsmesh.net',
-  community_mqtt_broker_port: 443,
-  community_mqtt_email: '',
   flood_scope: '',
   blocked_keys: [],
   blocked_names: [],