RFR (S) 8208575: Remove Atomic::add/sub for short

[coleen.phillimore at oracle.com]

Summary: Removed code to atomic::add for short because it's no longer 
used for Symbol.

open webrev at http://cr.openjdk.java.net/~coleenp/8208575.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8208575

Ran hs-tier1-3

Thanks,
Coleen