chore: fix lint warnings

Fixes a few lint warnings that got into master.

Author: crisbeto

src/lib/tabs/tab-body.ts

@@ -24,14 +24,7 @@ import {
   forwardRef,
   ViewChild,
 } from '@angular/core';
-import {
-  trigger,
-  state,
-  style,
-  animate,
-  transition,
-  AnimationEvent,
-} from '@angular/animations';
+import {AnimationEvent} from '@angular/animations';
 import {TemplatePortal, CdkPortalOutlet, PortalHostDirective} from '@angular/cdk/portal';
 import {Directionality, Direction} from '@angular/cdk/bidi';
 import {Subscription} from 'rxjs/Subscription';

src/lib/tabs/tab.ts

@@ -51,7 +51,7 @@ export class MatTab extends _MatTabMixinBase implements OnInit, CanDisable, OnCh
    */
   @ContentChild(MatTabContent, {read: TemplateRef}) _explicitContent: TemplateRef<any>;
 
-  /** Template inside the MatTab view that contains an <ng-content>. */
+  /** Template inside the MatTab view that contains an `<ng-content>`. */
   @ViewChild(TemplateRef) _implicitContent: TemplateRef<any>;
 
   /** The plain text label for the tab, used when there is no template label. */