Remove accidentally added test data files

In commit 352e3122 (Add test for vtkOpenFOAMReader, 2013-12-24) we
accidentally added files prefixed in "._" in addition to the actual data
files.  These files aren't real and, when you archive and untar a vtk
release, produce file exists warnings.

Change-Id: I13b600357f1b9712d55d8c0284c97fd1b0255683