RFR: 8214786: Remove unused ThreadLocalAllocBuffer::verify()

[Per Liden]

The function ThreadLocalAllocBuffer::verify() is never used and can be 
removed. It's also potentially dangerous to use, as the verification 
currently done there steps out into the heap without honoring barrier/GC 
rules.

Bug: https://bugs.openjdk.java.net/browse/JDK-8214786
Webrev: http://cr.openjdk.java.net/~pliden/8214786/webrev.0

/Per