RFR(T) : 8250797 : remove CompileReason::Reason_CTW

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8250797/webrev.00
> 5 lines changed: 0 ins; 4 del; 1 mod; 

Hi all,

could you please review this patch?
from JBS:
> "native" CTW has been removed by JDK-8213812 (JDK-8214917), so CompileReason::Reason_CTW isn't used anymore and should be removed.

besides removing CompileReason::Reason_CTW and corresponding element from reason_names[] array, the patch also updates the comment for CompileReason as CompileTask::can_become_stale doesn't really depend on the order.

webrev: 
JBS: https://bugs.openjdk.java.net/browse/JDK-8250797

-- Igor