Remove feature_dnd

Rationale: it's a poor implementation and will conflict with proper feature development.

src/settings/Settings.tsx

@@ -201,13 +201,6 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         supportedLevels: LEVELS_FEATURE,
         default: false,
     },
-    "feature_dnd": {
-        isFeature: true,
-        labsGroup: LabGroup.Profile,
-        displayName: _td("Show options to enable 'Do not disturb' mode"),
-        supportedLevels: LEVELS_FEATURE,
-        default: false,
-    },
     "feature_latex_maths": {
         isFeature: true,
         labsGroup: LabGroup.Messaging,
@@ -344,11 +337,6 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         displayName: _td("Show current avatar and name for users in message history"),
         default: false,
     },
-    "doNotDisturb": {
-        supportedLevels: [SettingLevel.DEVICE],
-        default: false,
-        controller: new IncompatibleController("feature_dnd", false, false),
-    },
     "mjolnirRooms": {
         supportedLevels: [SettingLevel.ACCOUNT],
         default: [],