RFR: 8231051: Remove check_obj_alignment() and replace with is_object_aligned()

[Per Liden]

We have a check_obj_alignment() function in oopsHierarchy.hpp. This 
function can be removed and the calls to it can be replaced by calls the 
more common is_object_aligned(), which does the same thing.

Bug: https://bugs.openjdk.java.net/browse/JDK-8231051
Webrev: http://cr.openjdk.java.net/~pliden/8231051/webrev.0

Testing: Currently running though tier-1

/Per