runtime: delete native/java_lang_Runtime.cc

We're now using Runtime.c from ojluni, which does the same set
of things via the JVM interface. This removes unnecessary duplication
of code between Runtime.cc and OpenJdkJvm.cc.

Also includes a few changes to JVM_NativeLoad to bring it in sync
with the version in Runtime.cc.

bug: 27387202
Change-Id: I92aac81d131661aca588e352aee7a167593e17d4