RFR (XXS) 8213760: os::obsolete_option is obsolete and should be removed

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8213760
webrev: http://cr.openjdk.java.net/~dholmes/8213760/webrev/

We've been flagging a small set of non-existent -X options as obsolete 
for the past 16 years on Solaris only. That's probably enough time for 
people to update their scripts.

More info in bug report but the flags are:

-Xt
-Xmt
-Xverifyheap

and -Xmaxjitcodesize was also listed but not actually being treated as 
obsolete.

The mechanism for per-OS obsoletion of -X flags is not needed and is 
removed.

Thanks,
David