I have had a look in the admin console and no options to hide a welcome screen or to preset location.
Much like other software and browser based products it's just a one time thing that needs to be adhered to.
Sorry, I can't provide a different answer or a solution to removing it. I'm also happy to be proven wrong but as part of the set up of the product, this always occurs. I have seen several users set Flow up in my org and no way round it even when location is specifically set in O365.
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