Remove docs and config for invite only padlocks

See https://github.com/matrix-org/matrix-react-sdk/pull/4488

docs/labs.md

@@ -87,11 +87,6 @@ tab as the single source of truth just yet.
 This adds a presence indicator in the room list next to DM rooms where the other
 person is online.
 
-## Show padlocks on invite only rooms (`feature_invite_only_padlocks`)
-
-This adds padlocks to room list tiles and room header for invite only rooms.
-This feature flag (unlike most) is enabled by default.
-
 ## Custom themes (`feature_custom_themes`)
 
 Custom themes are possible through Riot's [theme support](./theming.md), though

riot.im/develop/config.json

@@ -21,7 +21,6 @@
         "feature_mjolnir": "labs",
         "feature_dm_verification": "labs",
         "feature_cross_signing": "enable",
-        "feature_invite_only_padlocks": "enable",
         "feature_bridge_state": "labs",
         "feature_presence_in_room_list": "labs",
         "feature_custom_themes": "labs"