Fix OpenSSLSessionImpl.getCreationTime and getLastAccessedTime.

Fix OpenSSLSessionImpl.getCreationTime and getLastAccessedTime.

This addresses one part of this abandoned change from ursg:
  https://android-git.corp.google.com/g/4743

I've also tidied up the native method names to use the harmony "-Impl"
convention, removed useless methods that just forward to a native method,
and removed dead code. I've canonicalized some of the duplication too,
but I want to go through the rest of out OpenSSL code before I really start
trying to remove the duplication.

When this is submitted, I'll fix the other (unrelated) bug the abandoned
change addressed.