[FIX][partner_ref_unique] Work with contact deduplicator.

[yajo]

This contraint is self-disabled when it detects by context that it is being used from the contact deduplicator.

Otherwise, the user cannot deduplicate a contact selecting the "good" one as the one without reference.

Anyway, in these cases, the check has no meaning, since it is to avoid duplicates and in this context we are currently removing them.

@Tecnativa

[pedrobaeza]

:+1:, although you know that I don't share the whole point why this module is needed (about making unique the ref, which is useless) :wink:

[yajo]

I imagine they use it for a unique ID, but anyway we should not have bugs, useless or not.

[rafaelbn]

Done