overlay: remove srgb mode option

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <!-- IDs for each color mode. The values must match the corresponding constants in

         android.view.Display -->

    <integer-array name="color_mode_ids">

        <item>0</item>

        <item>-1</item>

        <item>-1</item>

    </integer-array>

</resources>