I agree with @CommonsWare that it is invalid design to hide the Done button.
However, there are customers that want to have this button removed and I can understand that the checkmark may cause confusion to users because it actually does nothing in some cases.
So, here is how to remove the button with styles:
<style name="AppTheme" parent="android:Theme.Holo">
<item name="android:actionModeCloseButtonStyle">@style/NoCloseButton</item>
</style>
<style name="NoCloseButton" parent="@android:style/Widget.ActionButton.CloseMode">
<item name="android:visibility">gone</item>
</style>
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…