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

(cherry picked from commit 5f971572)

Change-Id: Ic2848755505a0cb25da8237150b07dadf0a42929