Fix lint errors

Author: MichaelJamesParsons

src/cdk/scrolling/virtual-scroll-repeater.ts

@@ -7,7 +7,7 @@
  */
 
 import {Observable} from 'rxjs';
-import {ListRange} from '../collections';
+import {ListRange} from '@angular/cdk/collections';
 
 /**
  * An item to be repeated by the VirtualScrollViewport

src/cdk/scrolling/virtual-scroll-viewport.ts

@@ -34,7 +34,6 @@ import {
 import {auditTime, startWith, takeUntil} from 'rxjs/operators';
 import {ScrollDispatcher} from './scroll-dispatcher';
 import {CdkScrollable, ExtendedScrollToOptions} from './scrollable';
-import {CdkVirtualForOf} from './virtual-for-of';
 import {VIRTUAL_SCROLL_STRATEGY, VirtualScrollStrategy} from './virtual-scroll-strategy';
 import {ViewportRuler} from './viewport-ruler';
 import {CdkVirtualScrollRepeater} from './virtual-scroll-repeater';