G1 computes tenuring threshold before per GC according to the last age table and prints new age table after per GC. But the Serial GC computes tenuring threshold and prints new age table both after per GC. It causes the method `AgeTable::print_on` prints the wrong tenuring threshold.

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According to the discussion in the PR, it is better not to print the threshold in `AgeTable::print_on`. I will change the summary of this issue.