[el2p] get rid of HAVE_DUNE_PDELAB switches

PDElab is a requirement for el2p for a very long time now. Some switches
remained. This patch deletes them for consistency.



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@14238 2fb0f335-1f38-0410-981e-8018bf24f1b0