cad/freecad-devel: fix pkg-plist without webengine

pkg-static: Unable to access file /wrkdirs/usr/ports/cad/freecad-devel/work/stage/usr/local/FreeCAD/Mod/Web/Init.py:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/cad/freecad-devel/work/stage/usr/local/FreeCAD/lib/Web.so:No such file or directory