remove deprecated utilities

Summary: Remove `$Subtype` and `$Supertype` utilities. Replacement was done on a best-effort basis. In many cases it sufficed to replace `$Supertype<T>` and `$Subtype<T>` with `T`, but when this was not possible `any | T` and `any & T` were used instead.

Reviewed By: jbrown215

Differential Revision: D13624765

fbshipit-source-id: 82ee9d43cfc318ed4bd2d84e0f4c5c1d8f488a9c

src/reducers/index.js

@@ -36,6 +36,7 @@ import type {
 } from './plugins.js';
 import type {Store as ReduxStore} from 'redux';
 
+// $FlowFixMe introduced when removing $Subtype/$Supertype
 export type Store = ReduxStore<
   {|
     application: ApplicationState,