SA: delete dead code in jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ObjectHeap.java

After CMS collector is removed, the following code in jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/ObjectHeap.java of method iterateLiveRegions() :
```
    if (heap instanceof GenCollectedHeap) {
       GenCollectedHeap genHeap = (GenCollectedHeap) heap;
       Generation genOld = genHeap.getGen(1);
    }
```
should be removed too.