Remove FlowFixMe's from TypeScript

Summary: This diff was a joy to draft.

Reviewed By: jknoxville

Differential Revision: D17344676

fbshipit-source-id: 0694d0393fa243edef61408ecfee92912fbbfa32

src/dispatcher/tracking.tsx

@@ -6,7 +6,6 @@
  */
 
 import {ipcRenderer} from 'electron';
-// $FlowFixMe perf_hooks is a new API in node
 import {performance} from 'perf_hooks';
 
 import {Store} from '../reducers/index';