RFR (S) 8245754: Shenandoah: ditch ShenandoahAlwaysPreTouch

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8245754

ShenandoahAlwaysPreTouch flag dates back to the times when ShenandoahHeap used VirtualSpace for
reserving/committing heap. To workaround single-threaded pretouch code in VirtualSpace, a new flag
was needed:
 https://mail.openjdk.java.net/pipermail/shenandoah-dev/2016-October/000892.html

That code is long gone now, and current Shenandoah just reserves/commits from OS directly.
Therefore, this flag is no longer needed. It actually confuses logging in JDK-8245720.

Fix:
  https://cr.openjdk.java.net/~shade/8245754/webrev.01/

Testing: hotspot_gc_shenandoah {fastdebug,release}; ad-hoc runs

-- 
Thanks,
-Aleksey