Remove deprecated extra_taxonomy_validations preference

Ref solidusio#4851

core/app/models/spree/taxonomy.rb

@@ -5,7 +5,7 @@ class Taxonomy < Spree::Base
     acts_as_list
 
     validates :name, presence: true
-    validates :name, uniqueness: true, if: -> { Spree::Config.extra_taxonomy_validations }
+    validates :name, uniqueness: true
 
     has_many :taxons, inverse_of: :taxonomy
     has_one :root, -> { where parent_id: nil }, class_name: "Spree::Taxon", dependent: :destroy

core/lib/spree/app_configuration.rb

@@ -171,22 +171,6 @@ def allow_promotions_any_match_policy=(value)
     #   @return [Regexp] Regex to be used in email validations, for example in Spree::EmailValidator
     preference :default_email_regexp, :regexp, default: URI::MailTo::EMAIL_REGEXP
 
-    # @!attribute [rw] extra_taxonomy_validations
-    #   Use extra validations on Taxonomies in 3.4.0, but default to false so stores can
-    #   upgrade and then fix any now invalid Taxonomies before enabling.
-    #   @return [Boolean]
-    versioned_preference :extra_taxonomy_validations, :boolean, initial_value: false, boundaries: { "3.4.0.dev" => true }
-    def extra_taxonomy_validations=(value)
-      Spree::Deprecation.warn <<~MSG
-        Solidus will remove `Spree::Config.extra_taxonomy_validations` preference
-        in the next major release and will always use the extra Taxonomy validations.
-        Before upgrading to the next major, please fix any now invalid Taxons
-        and then remove the preference definition in `config/initializers/spree.rb`.
-      MSG
-
-      preferences[:extra_taxonomy_validations] = value
-    end
-
     # @!attribute [rw] generate_api_key_for_all_roles
     #   @return [Boolean] Allow generating api key automatically for user
     #   at role_user creation for all roles. (default: +false+)

core/spec/lib/spree/app_configuration_spec.rb

@@ -177,20 +177,4 @@ class DummyClass; end;
       expect(prefs.mails_from).to eq('[email protected]')
     end
   end
-
-  context 'extra_taxonomy_validations=' do
-    it 'is deprecated' do
-      expect(Spree::Deprecation).to receive(:warn).with(/Solidus will remove `Spree::Config.extra_taxonomy_validations`/)
-
-      prefs.extra_taxonomy_validations=(false)
-    end
-
-    it "still sets the value so that consumers aren't broken" do
-      Spree::Deprecation.silence do
-        prefs.extra_taxonomy_validations=(false)
-      end
-
-      expect(prefs.extra_taxonomy_validations).to eq(false)
-    end
-  end
 end