Test: delete child object to address memory leak. (#1863)

[ROCm/rccl commit: 9d3acffa5f]

projects/rccl/test/common/TestBed.cpp

@@ -537,6 +537,7 @@ namespace RcclUnitTesting
       {
         ERROR("Child process %d exited with code %d\n", childId, returnVal);
       }
+      delete(childList[childId]);
     }
 
     childList.clear();