[15] RFR 8244328: Shenandoah: move ShenandoahThreadLocalData::_disarmed_value initialization

[Zhengyu Gu]

Please review this small patch that removes disarmed_value setting from 
initialize_gclab. The value is independently set vs. 
ShenandoahCodeRoots::arm_nmethods(), has nothing to do with gclab 
initialization.


Bug: https://bugs.openjdk.java.net/browse/JDK-8244328
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8244328/webrev.00/

Test:
   hotspot_gc_shenandoah

Thanks,

-Zhengyu