do validity checks using  dense_nonpacked_validate directly

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/matrix@2996 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
forgotten for r2996: no longer needing d(sy|tr)Matrix_validate()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/matrix@2997 edb9625f-4e0d-4859-8d74-9fd3b1da38cb