DOC: Update vtkRandomHills documentation.

The documentation has been updated and the reference to
the deprecated function GenerateTheHills has been
removed in Evaluate()

Change-Id: I10f8be9373aae41b336ee274b5959723b4fbd114
Signed-off-by: Andrew Maclean <andrew.amaclean@gmail.com>
Merge topic 'doc_update_vtkParametricRandomHills' into master

728b6a6b DOC: Update vtkRandomHills documentation.