refactor(material/tooltip): remove explicit change detection

Now that `OnPush` is the default, we can remove it from the metadata.

Author: crisbeto

src/material/tooltip/tooltip.spec.ts

@@ -1607,7 +1607,6 @@ class ScrollableTooltipDemo {
             [matTooltipPosition]="position">
       Button
     </button>`,
-  changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [MatTooltipModule, OverlayModule],
 })
 class OnPushTooltipDemo {

src/material/tooltip/tooltip.ts

@@ -15,7 +15,6 @@ import {
 import {ESCAPE, hasModifierKey} from '@angular/cdk/keycodes';
 import {
   AfterViewInit,
-  ChangeDetectionStrategy,
   ChangeDetectorRef,
   Component,
   Directive,
@@ -961,7 +960,6 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
   templateUrl: 'tooltip.html',
   styleUrl: 'tooltip.css',
   encapsulation: ViewEncapsulation.None,
-  changeDetection: ChangeDetectionStrategy.OnPush,
   host: {
     '(mouseleave)': '_handleMouseLeave($event)',
     'aria-hidden': 'true',