[distr] removed <<- assignment in plot-methods_LebDec.R --- it did not help to fix the glitch with panel.first anyway, and later on RobAStBase complains about it

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/distr@966 edb9625f-4e0d-4859-8d74-9fd3b1da38cb