SystemUI: Resolve status bar VPN icon tints

 * Remove the layout VPN icon's tint to respect
    SignalClusterView.java/applyIconTint's tint

 * Matches the handling of the Airplane Mode icon

 * Results: Before and after: https://ibb.co/eZ5Pud

 * Test: Bright wallpaper with status bar contrasts:
    https://ibb.co/dxupSy

Change-Id: I44cec84815b7c989a68eab45eeb762d5014bd0f3