RFR: remove useless one line change in loopnode.cpp

[Roman Kennke]

Ok

Am 29. November 2018 09:46:06 MEZ schrieb Roland Westrelin <rwestrel at redhat.com>:
>
>http://cr.openjdk.java.net/~roland/shenandoah/useless-loopnode.cpp/webrev.00/
>
>assert can never trigger because first if branch is always taken for
>is_ShenandoahBarrier().
>
>Roland.