Remove FlowFixMe's from TypeScript

Summary: This diff was a joy to draft.

Reviewed By: jknoxville

Differential Revision: D17344676

fbshipit-source-id: 0694d0393fa243edef61408ecfee92912fbbfa32

src/Client.tsx

@@ -367,7 +367,6 @@ export default class Client extends EventEmitter {
           this.store.getState().plugins.devicePlugins.get(params.api);
         if (persistingPlugin && persistingPlugin.persistedStateReducer) {
           let pluginKey = `${this.id}#${params.api}`;
-          //$FlowFixMe
           if (persistingPlugin.prototype instanceof FlipperDevicePlugin) {
             // For device plugins, we are just using the device id instead of client id as the prefix.
             this.deviceSerial().then(