[Cart Ajax API] Removing "All count name are in your cart." inventory error response

We are removing the "All count name are in your cart." error response in favour of the exisiting "You can't add more name to the cart." error response in the Cart Ajax API.

Old behaviour:

• When all inventory of a variant are already in the cart and the client requests to add more of that variant to the cart, the error response description is "All count name are in your cart.", and the message is "Cart Error".
• When some of the inventory of a variant is in the cart and the client requests to add more of that variant to the cart, so that the total amount in the cart is more than the available inventory, the error response description and message is "You can't add more name to the cart."

New behaviour:

• When the client requests to add more than available inventory of a variant already in the cart the error response description and message is "You can't add more name to the cart."

This will affect the update.js, change.js, and add.js endpoints.