PayPal Pro - how to remove link to paypal
My understanding is that part of your agreement with PayPal is to offer the option to pay with PayPal.  While you could use jQuery to hide the button or alter CiviCRM's code to remove it from display, you've promised PayPal that you won't.

There are stories (urban legends or actual instances, I'm not sure) of PayPal going after folks who hide the Pay with PayPal button.

Even if you don't care about that, CiviCRM will never remove the button so long as it's required by the agreement, so any code you write will have to be maintained as you upgrade.  This is a real cost that you should weigh against this.

Separately, we have clients who swear that many of their donors prefer to use PayPal, so that's another reason to leave it as-is.