Removed the XML shaders and associated classes

These have not been used in quite some time, add dependencies on XML
in the core rendering API and have been superseded by their sequels.

Disabled GenericVertexAttributes tests for now due to use of XML
shader API, along with the materials object example.

Change-Id: I3c57c46b1d3cc7f550bd30e1abcd6e5d87347d36
vtkIOImage not needed by vtkRenderingCore now

Now that the XML shader stuff is gone the vtkIOImage library isn't
needed either.

Change-Id: I64adeabd461c5adfb3793450576460aa477bfab7
Removed vtkUtilitiesMaterialsLibrary

This is no longer needed/used.

Change-Id: I19ad4e59f654337b4cd7c125876e8323cd534454
Merge topic 'rendering-remove-xml' into master

6501ce8c Removed vtkUtilitiesMaterialsLibrary
4b96f6f3 vtkIOImage not needed by vtkRenderingCore now
67cb974b Removed the XML shaders and associated classes