remove unused include

Change-Id: Ia5a12fed570fcfc0db4e8080dd6cf3c2714293ab
bnc#882383: Add chart unit test for GradientName property.

It needs to be set, so that the chart has colors. It was grey before.
The bug was fixed already in aacfd5038d05a02f8b1eade3a5896d3d7e959f3d,
which got pushed sooner, so this commit only changes
the property name from 'INVALID' to 'FillTransparenceGradientName'.

Change-Id: If06899258a4307d583480538338480ba5bb830b9