This will make it so that the PayPal button does not display when registering for a specific event. In this example, the event ID is 74. You'll need to swap in your event ID that you don't want the PayPal button to appear for.

remove_paypal.php

<?php

function htrappfae_remove_paypal_from_event($payment_data) {
  extract( $payment_data );
	if ( $event_id==74 ) { //check to see if this is the event with the ID of #74
		remove_action( 'action_hook_espresso_display_offsite_payment_gateway', 'espresso_display_paypal' );
	}
}

add_action ( 'action_hook_espresso_display_offsite_payment_gateway', 'htrappfae_remove_paypal_from_event', 9 );