RFR(xs): 8198270: Remove dangerous assert in HandleArea::oops_do()

[Per Liden]

With the introduction of the Access API it's no longer safe to assume 
that you can safely de-reference an oop without using the proper Access 
function. The assert in HandleArea::oops_do() makes this assumption, 
which can lead to crashes. This patch removes the offending assert.

Bug: https://bugs.openjdk.java.net/browse/JDK-8198270
Webrev: http://cr.openjdk.java.net/~pliden/8198270/webrev.0/

/Per