OnlyNondegenerate -- restrict to nondegenerate geometric vertex decompositions

Set to true to restrict the output of findOneStepGVD to return only the indeterminates for which their geometric vertex decomposition is nondegenerate. Default value false. Following the notation of oneStepGVD, a geometric vertex decomposition is degenerate if either $\sqrt{C_{y, I}} = \sqrt{N_{y, I}}$ or if $C_{y, I} = \langle 1 \rangle$, and is nondegenerate otherwise.