Remove comment that claims tick interval defaults to auto

Author: iveysaur

src/components/slider/slider.ts

@@ -57,8 +57,7 @@ export class MdSlider implements AfterContentInit {
   @Input() step: number = 1;
 
   /**
-   * How often to show ticks. Defaults to auto which calculates how many to show.
-   * Relative to the step so that a tick always appears on a step.
+   * How often to show ticks. Relative to the step so that a tick always appears on a step.
    * Ex: Tick interval of 4 with a step of 3 will draw a tick every 4 steps (every 12 values).
    */
   private _tickInterval: 'auto' | number;