Prune unsupported setting RoomSubList.showEmpty

The code reading this setting was previously removed in #2229.

src/components/structures/UserSettings.js

@@ -82,7 +82,6 @@ const SIMPLE_SETTINGS = [
     { id: "VideoView.flipVideoHorizontally" },
     { id: "TagPanel.disableTagPanel" },
     { id: "enableWidgetScreenshots" },
-    { id: "RoomSubList.showEmpty" },
     { id: "pinMentionedRooms" },
     { id: "pinUnreadRooms" },
     { id: "showDeveloperTools" },

src/i18n/strings/en_EN.json

@@ -296,7 +296,6 @@
     "Pin rooms I'm mentioned in to the top of the room list": "Pin rooms I'm mentioned in to the top of the room list",
     "Pin unread rooms to the top of the room list": "Pin unread rooms to the top of the room list",
     "Enable widget screenshots on supported widgets": "Enable widget screenshots on supported widgets",
-    "Show empty room list headings": "Show empty room list headings",
     "Always invite users which may not exist": "Always invite users which may not exist",
     "Show developer tools": "Show developer tools",
     "Collecting app version information": "Collecting app version information",

src/settings/Settings.js

@@ -324,11 +324,6 @@ export const SETTINGS = {
         supportedLevels: ['room-device'],
         default: false,
     },
-    "RoomSubList.showEmpty": {
-        supportedLevels: LEVELS_ACCOUNT_SETTINGS,
-        displayName: _td('Show empty room list headings'),
-        default: true,
-    },
     "alwaysInviteUnknownUsers": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td('Always invite users which may not exist'),