RFR (T) 8225760: oop::raw_set_obj isn't needed

[coleen.phillimore at oracle.com]

Remove the public function and add to set_obj.  Ran tier1 tests locally.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8225760.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8225760

Thanks,
Coleen