Ok, so I decided to get with the program and try using discovery for MQTT. Being the cautious type I started with one Sonoff (which I call sonoff05). As usual in HA it doen’t seem to be plain sailing 
All did seem to be ok at first, except that in the entity registry I have two instances of this sonoff switch with one being suffixed with _2
The newly discovered sonoff is switch.sonof05_2 and what must be the pre-discovery version being switch.sonoff05.
How do I remove the ghost entity? It does not appear either in the MQTT Integration nor the new Entity registry UI.
In my ‘storage’, I have ONLY the following in core.entity_registry
"config_entry_id": "6bd29288c639478ea6cdcabfc9c8f2ee",
"device_id": "270baf0544e64284b55d71ef55eb72bd",
"disabled_by": null,
"entity_id": "binary_sensor.sonoff05_btn_2",
"name": null,
"platform": "mqtt",
"unique_id": "7A53EE_BTN_1"
(I don’t even know what binary_sensor.sonoff05_btn_2 is!)
And in core.restore_state I have BOTH this
"last_seen": "2019-02-15T15:50:59.014206+00:00",
"state": {
"attributes": {
"friendly_name": "Sonoff05"
},
"context": {
"id": "33b2d50897c74c389bd6f3064203096b",
"user_id": null
},
"entity_id": "switch.sonoff05",
"last_changed": "2019-02-15T15:32:47.613078+00:00",
"last_updated": "2019-02-15T15:32:47.613078+00:00",
"state": "off"
AND
"last_seen": "2019-02-15T15:50:59.014206+00:00",
"state": {
"attributes": {
"friendly_name": "Sonoff05"
},
"context": {
"id": "b55a04c6b51245ccaf1adb684f844783",
"user_id": null
},
"entity_id": "switch.sonoff05_2",
"last_changed": "2019-02-15T15:49:06.806896+00:00",
"last_updated": "2019-02-15T15:49:06.806896+00:00",
"state": "on"
