Remove non-Sandy UI

Summary:
This removes the Non-Sandy UI from the Flipper codebase. It is a pretty rough scan for unused components, over time when converting more advanced components to Ant design probably even more code can be removed.

Partially used `npx ts-purge` to reveal never imported source files.

Changelog: It is no longer possible to opt out of the new Sandy UI

Reviewed By: jknoxville

Differential Revision: D25825282

fbshipit-source-id: 9041dbc7e03bce0760c9a0a34f1877851b5f06cf

desktop/app/src/Client.tsx

@@ -14,7 +14,6 @@ import {
   FlipperDevicePlugin,
 } from './plugin';
 import BaseDevice, {OS} from './devices/BaseDevice';
-import {LegacyApp} from './chrome/LegacyApp';
 import {Logger} from './fb-interfaces/Logger';
 import {Store} from './reducers/index';
 import {setPluginState} from './reducers/pluginStates';
@@ -124,7 +123,6 @@ export interface FlipperClientConnection<D, M> {
 }
 
 export default class Client extends EventEmitter {
-  app: LegacyApp | undefined;
   connected: boolean;
   id: string;
   query: ClientQuery;