Replace MTTM Performance Indicator by OMRT and OMA in engineering job families

Why is this change being made?

The Mean Time to Merge (MTTM) Performance Indicator has been removed in !85837 (merged) and replaced with Open MR Age (OMA) and Open MR Review Time (OMRT) as better indicators of efficiency/productivity.

This MR updates the job families in engineering division to reflect this change.

Note that this MR only updates one page for now to start the conversation. Once approved we'll replicate the change to all other pages.

refs #12307 (closed)

Author Checklist

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• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
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