RFR 15 (S) 8231559: Remove expired flags in JDK 15

[Kim Barrett]

> On Dec 12, 2019, at 11:51 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
> It is that time of the release again. All the expired entries in the flag table can be deleted.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8231559
> webrev: http://cr.openjdk.java.net/~dholmes/8231559/webrev/
> 
> It's mostly all the old CMS flags.
> 
> Thanks,
> David

Looks good.

This change also fixes https://bugs.openjdk.java.net/browse/JDK-8232739.