[REF] Tighten up function signature for dedupePair

[eileenmcnaughton]

Overview

This gets rid of the confusing keys earlier and ensures they are integers. It's only called from
one place (which is heavily tested) so the signature can be changed like this

Before

$dupes passed in but it only holds 2 poorly named parameters

After

Parameters passed in directly

Technical Details

I'm preparing to add an apiv4 function for this

Comments

Lots of tests cover this

[civibot]

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[eileenmcnaughton]

@colemanw can you merge this - I was looking to add a v4 api for merge & this is preliminary cleanup

[seamuslee001]

Tests would fail if this was a problem merging