Remove unused presenter

The usage of this presenter got removed seven years ago:
c5d031a6d7

app/presenters/variant_presenter.rb

@@ -1,13 +0,0 @@
-class VariantPresenter
-  attr_accessor :variant
-
-  def initialize(variant)
-    @variant = variant
-  end
-
-  delegate :id, to: :variant
-
-  def image_url
-    @variant.images.first.attachment.url :mini if @variant.images.present?
-  end
-end