Optimize package handling for archived classes

InstanceKlass::set_package():

http://hg.openjdk.java.net/jdk/jdk/file/0edc7fd0d7a3/src/hotspot/share/oops/instanceKlass.cpp#l2700

No need to check prohibited packages for shared classes (we don't archive prohibited classes).

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SystemDictionary::load_shared_class()

http://hg.openjdk.java.net/jdk/jdk/file/0edc7fd0d7a3/src/hotspot/share/classfile/systemDictionary.cpp#l1342

  if (class_loader.is_null()) {
    int path_index = ik->shared_classpath_index();
    ResourceMark rm;
    ClassLoader::add_package(ik->name()->as_C_string(), path_index, THREAD);
  }

This call really only does this:

   pkg_entry->set_classpath_index(ik->classpath_index);

so we can move this code into InstanceKlass::set_package().