Remove shadow below actionbar

I use actionbarsherlock. The piece of code below is responsible for changing it’s background to a custom one.

<style name="Widget.Styled.ActionBar" parent="Widget.Sherlock.ActionBar">
    <item name="background">@drawable/actionbar_bg</item>
    <item name="android:background">@drawable/actionbar_bg</item>
    <...>  
</style>

<style name="Theme.MyApp" parent="@style/Theme.Sherlock.Light">
    <item name="actionBarStyle">@style/Widget.Styled.ActionBar</item>
    <item name="android:actionBarStyle">@style/Widget.Styled.ActionBar</item>
    <..>
</style>

And it works for actionbarsherlock (on versions below honeycomb). But in ICS I have a shadow below actionbar which I don’t want. What is the style item to make it disappear?