Remove extensible events v1 experimental rendering (#9881)

* Remove extensible events v1 experimental rendering

With the changes to extensible events in v2 largely being contained to a room version, we don't need to have this code or the labs flag anymore. If the labs flag becomes useful in the future, it will be re-added.

* Run prettier

src/settings/Settings.tsx

@@ -340,13 +340,6 @@ export const SETTINGS: { [setting: string]: ISetting } = {
         supportedLevels: LEVELS_FEATURE,
         default: false,
     },
-    "feature_extensible_events": {
-        isFeature: true,
-        labsGroup: LabGroup.Developer, // developer for now, eventually Messaging and default on
-        supportedLevels: LEVELS_FEATURE,
-        displayName: _td("Show extensible event representation of events"),
-        default: false,
-    },
     "useOnlyCurrentProfiles": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td("Show current avatar and name for users in message history"),