Allow to use setShippingProfile method to remove the profile

Problem/Motivation

Wishlist API allows to set the Shipping Profile related to the wishlist. However, it is not possible to unset the value, given that method only allows to pass ProfileInterface objects as parameters.

Steps to reproduce

Create a Wishlist and a Profile
Set the profile $wishlist->setShippingProfile($profile)->save()
Try to unset the profile $wishlist->setShippingProfile(NULL)->save()
Exceptions thrown: TypeError: Drupal\commerce_wishlist\Entity\Wishlist::setShippingProfile(): Argument #1 ($profile) must be of type Drupal\profile\Entity\ProfileInterface

Proposed resolution

Allow to pass NULL as parameter to unset the profile.