chore(admin): Remove unsed constant

Never used and bad practice anyway. Use CSS
for spacing not HTML 4 hacks.

Author: tvdeyen

admin/app/components/solidus_admin/orders/show/adjustments/index/component.rb

@@ -13,8 +13,6 @@ def title
     t(".title", number: @order.number)
   end
 
-  NBSP = " ".html_safe
-
   def initialize(order:, adjustments:)
     @order = order
     @adjustments = adjustments