Revert "[CMake][ParMETIS] Fix some typos in dune_register_package_flags() call"

This reverts commit 5f053401.

I was a little hasty in cherry-picking this from the dune_enable_all_packages()
branch, as it needs some infrastructure from over there.

cmake/modules/FindParMETIS.cmake

@@ -98,9 +98,10 @@ if(PARMETIS_FOUND)
     "Library directory: ${PARMETIS_LIBRARIES}\n\n")
 endif(PARMETIS_FOUND)
 
-# register all ParMETIS related flags
+#add all parmetis related flags to ALL_PKG_FLAGS, this must happen regardless of a target using add_dune_parmetis_flags
 if(PARMETIS_FOUND)
-  dune_register_package_flags(COMPILE_DEFINITIONS "ENABLE_PARMETIS=1"
-                              LIBRARIES "${PARMETIS_LIBRARIES}"
-                              INCLUDE_DIRS "${PARMETIS_INCLUDE_DIRS}")
+  foreach(dir ${PARMETIS_INCLUDE_DIRS})
+    set_property(GLOBAL APPEND PROPERTY ALL_PKG_FLAGS "-I${dir}")
+  endforeach()
+  set_property(GLOBAL APPEND PROPERTY ALL_PKG_LIBS "${PARMETIS_LIBRARIES}")
 endif()