RFR(xs): 8076534: CollectedHeapName in SA agent incorrect

[Per Liden]

Hi,

Could I please have someone review this minor fix.

In a recent change made to CollectedHeap::Name, the Abstract member was 
removed (JDK-8076294). This patch removes the equivalent from the SA 
agent's CollectedHeapName and turns its CollectedHeap into an abstract 
class.

Webrev: http://cr.openjdk.java.net/~pliden/8076534/webrev.0/

Bug: https://bugs.openjdk.java.net/browse/JDK-8076534

Testing: jprt, manual runs with jmap -F -heap with all collectors

/Per