docs: remove section on updating cart's customer (#10154)

* docs: add more clarification on updating a cart's customer

* remove section

www/apps/resources/app/storefront-development/cart/create/page.mdx

@@ -118,7 +118,3 @@ This is necessary, as only products matching the cart's sales channel(s) can be
 ## Associate Customer with Cart
 
 When the cart is created for a logged-in customer, it's automatically associated with that customer.
-
-If the customer is a guest, then later logs in, you can set their ID on the cart by updating it.
-
-Refer to [this documentation](../update/page.mdx#update-carts-customer) to learn how to set the customer of a cart.

www/apps/resources/app/storefront-development/cart/update/page.mdx

@@ -46,44 +46,3 @@ fetch(`http://localhost:9000/store/carts/${cartId}`, {
 ```
 
 The Update Cart API route accepts a `region_id` request body parameter, whose value is the new region to associate with the cart.
-
----
-
-## Update Cart's Customer
-
-If a guest customer logs in, you must update the cart to be associated with the logged-in customer.
-
-<Note>
-
-You can't change the `customer_id` if the cart was associated with a customer previously.
-
-</Note>
-
-For example:
-
-export const updateCustomerHighlights = [
-  ["11", `"logged_in_id"`, "Pass the logged-in customer's ID."]
-]
-
-```ts highlights={updateCustomerHighlights}
-fetch(`http://localhost:9000/store/carts/${cartId}`, {
-  credentials: "include",
-  method: "POST",
-  headers: {
-    "Content-Type": "application/json",
-    headers: {
-      "x-publishable-api-key": process.env.NEXT_PUBLIC_MEDUSA_PUBLISHABLE_KEY,
-    },
-  },
-  body: JSON.stringify({
-    customer_id: "logged_in_id",
-  }),
-})
-.then((res) => res.json())
-.then(({ cart }) => {
-  // use cart...
-  console.log(cart)
-})
-```
-
-The Update Cart API route accepts a `customer_id` request body parameter, whose value is the customer to associate with the cart.