Fixed issue of possibly modifying other polydatas.

The way that RemoveDeletedCells() or RemoveGhostCells() was
implemented it had the potential to modify data members that
were shared with other polydatas. This could cause filters to
modify their inputs accidentally as well. This was changed so
that these methods would create new data member objects that
would be modified.

Change-Id: I1939ea011ca5bc6c147d9b0b3af04731959127d0
Merge topic '0014459-RemoveDeletedCells-3' into master

cfaedbb0 Fixed issue of possibly modifying other polydatas.