chore: re-export symbols in core/platform (#2216)

src/lib/core/core.ts

@@ -30,9 +30,7 @@ export {DomPortalHost} from './portal/dom-portal-host';
 export * from './projection/projection';
 
 // Platform
-export * from './platform/platform';
-export * from './platform/features';
-export {PlatformModule} from './platform/index';
+export * from './platform/index';
 
 // Overlay
 export {Overlay, OVERLAY_PROVIDERS} from './overlay/overlay';

src/lib/core/platform/index.ts

@@ -1,6 +1,9 @@
 import {NgModule, ModuleWithProviders} from '@angular/core';
 import {MdPlatform} from './platform';
 
+export * from './platform';
+export * from './features';
+
 
 @NgModule({})
 export class PlatformModule {