ClipAndDrawGradientToBounds no longer required

Now that we have removed XORClipAndDrawGradient, there is no need
for the function ClipAndDrawGradientToBounds because the sole
purpose of that function was to work out whether the system should
use XOR clipping or not for gradients!

Change-Id: Id29b804054dfc30a9cc350bf4958ea3b2420e272