Removes unnecessary calls to zeitwerk_enabled?

In Rails 7 zeitwerk_enabled? returns true unconditionally. It exists to let 3rd
party code supporting multiple Rails versions check, but we no longer need to use
it internally.

railties/lib/rails/application.rb

@@ -513,11 +513,7 @@ module Rails
 
     # Eager loads the application code.
     def eager_load!
-      if Rails.autoloaders.zeitwerk_enabled?
-        Rails.autoloaders.each(&:eager_load)
-      else
-        super
-      end
+      Rails.autoloaders.each(&:eager_load)
     end
 
   protected

railties/lib/rails/autoloaders.rb

@@ -9,28 +9,22 @@ module Rails
       include Enumerable
 
       def main
-        if zeitwerk_enabled?
-          @main ||= Zeitwerk::Loader.new.tap do |loader|
-            loader.tag = "rails.main"
-            loader.inflector = ActiveSupport::Dependencies::ZeitwerkIntegration::Inflector
-          end
+        @main ||= Zeitwerk::Loader.new.tap do |loader|
+          loader.tag = "rails.main"
+          loader.inflector = ActiveSupport::Dependencies::ZeitwerkIntegration::Inflector
         end
       end
 
       def once
-        if zeitwerk_enabled?
-          @once ||= Zeitwerk::Loader.new.tap do |loader|
-            loader.tag = "rails.once"
-            loader.inflector = ActiveSupport::Dependencies::ZeitwerkIntegration::Inflector
-          end
+        @once ||= Zeitwerk::Loader.new.tap do |loader|
+          loader.tag = "rails.once"
+          loader.inflector = ActiveSupport::Dependencies::ZeitwerkIntegration::Inflector
         end
       end
 
       def each
-        if zeitwerk_enabled?
-          yield main
-          yield once
-        end
+        yield main
+        yield once
       end
 
       def logger=(logger)

railties/lib/rails/engine.rb

@@ -482,17 +482,8 @@ module Rails
     end
 
     def eager_load!
-      # Already done by Zeitwerk::Loader.eager_load_all. We need this guard to
-      # easily provide a compatible API for both zeitwerk and classic modes.
-      return if Rails.autoloaders.zeitwerk_enabled?
-
-      config.eager_load_paths.each do |load_path|
-        # Starts after load_path plus a slash, ends before ".rb".
-        relname_range = (load_path.to_s.length + 1)...-3
-        Dir.glob("#{load_path}/**/*.rb").sort.each do |file|
-          require_dependency file[relname_range]
-        end
-      end
+      # Already done by Zeitwerk::Loader.eager_load_all. By now, we leave the
+      # method as a no-op for backwards compatibility.
     end
 
     def railties

railties/lib/rails/tasks/zeitwerk.rake

@@ -1,11 +1,5 @@
 # frozen_string_literal: true
 
-ensure_zeitwerk_mode = ->() do
-  unless Rails.autoloaders.zeitwerk_enabled?
-    abort "Please, enable :zeitwerk mode in config/application.rb and try again."
-  end
-end
-
 eager_load = ->() do
   puts "Hold on, I am eager loading the application."
   Zeitwerk::Loader.eager_load_all