Removing "primary contacts" as option from activities Name field

[Joe BB]

Hello,

in our organization, we do not want prior account owners of accounts to see their old accounts that have been transferred to new owners.
Therefore,  we are going to transfer all Opportunities and Contacts to the current Account owners to which these Opps and Contacts pertain.

However, I just noticed that if we transfer all Contacts pertaining to an account to their current Account owners, the Activities that have a contact assigned as a "Primary Coontact" will be transferred as well to the new contact owner.
We do not want activities to be transferred, because we have Sales reps that share the same accounts with the owners of those accounts and we want the activities created by different Sales reps taht share accounts to remain under their ownership.
Is there a way to disable “Primary Contact” for Activities? Or is there a workaround?
 
Thank you!!!