WHAT

Once all usage of the old name of this metric has been removed, it can be renamed to the new name in the JMX exporter config in fleetshard, and the old partition and topic label keys can be removed from it

WHY

So that we don't have so many layers of unnecessary indirection

HOW

• Update the metric name in the JMX config here in fleetshard.
• Remove the old topic and partition labels, since the newer equivalents are in use everywhere now.