Remove class Spree::StockLocation

The database table is still there and can stay for a while until we are
confident that nothing is broken in production.

app/models/spree/stock_location.rb

@@ -1,13 +0,0 @@
-# frozen_string_literal: true
-
-module Spree
-  class StockLocation < ApplicationRecord
-    self.belongs_to_required_by_default = false
-    self.ignored_columns += [:backorderable_default, :active]
-
-    belongs_to :state, class_name: 'Spree::State'
-    belongs_to :country, class_name: 'Spree::Country'
-
-    validates :name, presence: true
-  end
-end