chore(overlay): unimplemented relative position strategy (#4446)

src/lib/core/overlay/position/relative-position-strategy.ts

@@ -1,16 +0,0 @@
-import {PositionStrategy} from './position-strategy';
-import {ElementRef} from '@angular/core';
-
-/** @docs-private */
-export class RelativePositionStrategy implements PositionStrategy {
-  constructor(private _relativeTo: ElementRef) { }
-
-  apply(element: Element): Promise<void> {
-    // Not yet implemented.
-    return null;
-  }
-
-  dispose() {
-    // Not yet implemented.
-  }
-}