Various cleanups in the generation of simgrid.jar

Various cleanups in the generation of simgrid.jar

- Only generate a simgrid.jar (kill simgrid_full.jar), which may or
  may not contain the native libs depending on the enable_lib_in_jar
  cmake option.
- Simplify the dependencies by not using temp files and additional
  dependencies but use add_custom_command(TARGET blah POST-BUILD ...)