refactor(material/stepper): remove explicit change detection

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

Author: crisbeto

src/material/stepper/step-header.ts

@@ -8,7 +8,6 @@
 
 import {FocusMonitor, FocusOrigin} from '@angular/cdk/a11y';
 import {
-  ChangeDetectionStrategy,
   ChangeDetectorRef,
   Component,
   Input,
@@ -39,7 +38,6 @@ import {_CdkPrivateStyleLoader, _VisuallyHiddenLoader} from '@angular/cdk/privat
     'role': '', // ignore cdk role in favor of setting appropriately in html
   },
   encapsulation: ViewEncapsulation.None,
-  changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [MatRipple, NgTemplateOutlet, MatIcon],
 })
 export class MatStepHeader extends CdkStepHeader implements AfterViewInit, OnDestroy {

src/material/stepper/stepper.ts

@@ -10,7 +10,6 @@ import {CdkStep, CdkStepper} from '@angular/cdk/stepper';
 import {
   AfterContentInit,
   AfterViewInit,
-  ChangeDetectionStrategy,
   Component,
   ContentChild,
   ContentChildren,
@@ -52,7 +51,6 @@ import {MatStepContent} from './step-content';
   ],
   encapsulation: ViewEncapsulation.None,
   exportAs: 'matStep',
-  changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [CdkPortalOutlet],
   host: {
     'hidden': '', // Hide the steps so they don't affect the layout.
@@ -134,7 +132,6 @@ export class MatStep extends CdkStep implements ErrorStateMatcher, AfterContentI
   },
   providers: [{provide: CdkStepper, useExisting: MatStepper}],
   encapsulation: ViewEncapsulation.None,
-  changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [NgTemplateOutlet, MatStepHeader],
 })
 export class MatStepper extends CdkStepper implements AfterViewInit, AfterContentInit, OnDestroy {