RFR(XS): 8245864: Obsolete BranchOnRegister

[Mikael Vidstedt]

Please review this small change which obsoletes the BranchOnRegister flag:

JBS: https://bugs.openjdk.java.net/browse/JDK-8245864
webrev: http://cr.openjdk.java.net/~mikael/webrevs/8245864/webrev.00/open/webrev/
CSR: https://bugs.openjdk.java.net/browse/JDK-8245865

Background (from JBS):

With Solaris removed (JDK-8241787) the BranchOnRegister flag no longer has any effect and should be removed using the normal process. Since the flag was really only useful on Solaris and since all the code it once controlled is now gone the flag will go directly to obsolete, skipping the deprecation step.

Testing:

* Manual verification running with the flag: spits out the warning as expected
* tier1: in progress

Cheers,
Mikael