Fix for issue 3455 (error when deleting vlv index)

The problem is caused because VLVIndex.close() is called twice.  VLVIndex.close() basically calls DatabaseContainer.close(), and calling it twice generates a NullPointerException (the database object is set to null when close() is called).

The fix consists on removing the first explicit call to VLVIndex.close (the next call to deleteDatabase(VLVIndex) will call VLVIndex.close).