RFR (XXS): 8134858: Remove G1 specific checking of Young/OldPLABSize in G1CollectorPolicy constructor

[Thomas Schatzl]

Hi all,

  can I have reviews for this small change that removes obsolete code?

JDK-8078555 added validation of Young/OldPLABSize values, and also the
bounds used here (raw region word size) are wrong.

CR:
https://bugs.openjdk.java.net/browse/JDK-8134858
Webrev:
http://cr.openjdk.java.net/~tschatzl/8134858/webrev/
Testing:
jprt

Thanks,
  Thomas