History:

The JVM claimed SIGUSR1 and SIGUSR2 for the INTERRUPT and ASYNC signals, respectively/

-XX:+UseAltSigs was provided to allow users to reclaim those signals and instead use two of the real-time signal (between SIGRTMIN and SIGRTMAX)

As of Solaris 10, Solaris provides SIGJVM1 and SIGJVM2 exclusively for the JVMs use. This avoids any conflict with user-defined signal usage.

As we no longer support Solaris versions older than 10, we do not need the UseAltSigs functionality and the flag can be made Obsolete.