Unfortunately, there isn't a way to control this from logic apps itself. Instead, you would want to front your SOAP service with a proxy that handles this for you.
In the cloud, you could use Azure APIM which can strip headers from being forwarded to your SOAP service. You can also deploy APIM in a VNET for it to access sources on-premises via a VPN Gateway or an Express Route connection.
But with the data gateway, you could leverage something like nginx. This answer mentions how you can remove client headers.
Also, you can leverage the self-hosted APIM gateway with the data gateway but this is available only in the premium and developer tiers of APIM.