Remove scroll behavior so it uses default.

CSSOM-View has removed the behaviour from ScrollIntoView dictionary.
This change updates to remove it from our scroll and means that browsers
should default to `auto` as described in CSSOM-View

Author: AutomatedTester

index.html

@@ -3995,9 +3995,6 @@ <h2>Elements</h2>
   the following <a><code>ScrollIntoViewOptions</code></a>:
 
   <dl>
-   <dt>"<code>behavior</code>"
-   <dd>"<code>instant</code>"
-
    <dt><a>Logical scroll position "<code>block</code>"</a>
    <dd>"<code>end</code>"