Remove AS methods that are never invoked

Fixes #21122 - does not change any current behavior; simply reflects
the fact that two conditions of the if/else statement are never reached.

The reason is #17227 which adds a default terminator to AS::Callbacks.

Therefore, even callback chains that do not define a terminator now
have a terminator, and `chain_config.key?(:terminator)` is always true.

Of course, if no terminator was defined, then we want this new default
terminator not to do anything special. What the terminator actually does
(or should do) is discussed in #21218 but the simple fact that a default
terminator exists makes this current PR valid.

*Note* that the conditional/simple methods have not been removed in
AS::Conditionals::Filter::After because of `:skip_after_callbacks_if_terminated`
which lets a user decide **not** to skip after callbacks even if the chain was
terminated.

activesupport/lib/active_support/callbacks.rb

@@ -126,14 +126,10 @@ class Before
         def self.build(callback_sequence, user_callback, user_conditions, chain_config, filter)
           halted_lambda = chain_config[:terminator]
 
-          if chain_config.key?(:terminator) && user_conditions.any?
+          if user_conditions.any?
             halting_and_conditional(callback_sequence, user_callback, user_conditions, halted_lambda, filter)
-          elsif chain_config.key? :terminator
-            halting(callback_sequence, user_callback, halted_lambda, filter)
-          elsif user_conditions.any?
-            conditional(callback_sequence, user_callback, user_conditions)
           else
-            simple callback_sequence, user_callback
+            halting(callback_sequence, user_callback, halted_lambda, filter)
           end
         end
 
@@ -175,42 +171,15 @@ def self.halting(callback_sequence, user_callback, halted_lambda, filter)
           end
         end
         private_class_method :halting
-
-        def self.conditional(callback_sequence, user_callback, user_conditions)
-          callback_sequence.before do |env|
-            target = env.target
-            value  = env.value
-
-            if user_conditions.all? { |c| c.call(target, value) }
-              user_callback.call target, value
-            end
-
-            env
-          end
-        end
-        private_class_method :conditional
-
-        def self.simple(callback_sequence, user_callback)
-          callback_sequence.before do |env|
-            user_callback.call env.target, env.value
-
-            env
-          end
-        end
-        private_class_method :simple
       end
 
       class After
         def self.build(callback_sequence, user_callback, user_conditions, chain_config)
           if chain_config[:skip_after_callbacks_if_terminated]
-            if chain_config.key?(:terminator) && user_conditions.any?
+            if user_conditions.any?
               halting_and_conditional(callback_sequence, user_callback, user_conditions)
-            elsif chain_config.key?(:terminator)
-              halting(callback_sequence, user_callback)
-            elsif user_conditions.any?
-              conditional callback_sequence, user_callback, user_conditions
             else
-              simple callback_sequence, user_callback
+              halting(callback_sequence, user_callback)
             end
           else
             if user_conditions.any?
@@ -273,14 +242,10 @@ def self.simple(callback_sequence, user_callback)
 
       class Around
         def self.build(callback_sequence, user_callback, user_conditions, chain_config)
-          if chain_config.key?(:terminator) && user_conditions.any?
+          if user_conditions.any?
             halting_and_conditional(callback_sequence, user_callback, user_conditions)
-          elsif chain_config.key? :terminator
-            halting(callback_sequence, user_callback)
-          elsif user_conditions.any?
-            conditional(callback_sequence, user_callback, user_conditions)
           else
-            simple(callback_sequence, user_callback)
+            halting(callback_sequence, user_callback)
           end
         end
 
@@ -318,33 +283,6 @@ def self.halting(callback_sequence, user_callback)
           end
         end
         private_class_method :halting
-
-        def self.conditional(callback_sequence, user_callback, user_conditions)
-          callback_sequence.around do |env, &run|
-            target = env.target
-            value  = env.value
-
-            if user_conditions.all? { |c| c.call(target, value) }
-              user_callback.call(target, value) {
-                run.call.value
-              }
-              env
-            else
-              run.call
-            end
-          end
-        end
-        private_class_method :conditional
-
-        def self.simple(callback_sequence, user_callback)
-          callback_sequence.around do |env, &run|
-            user_callback.call(env.target, env.value) {
-              run.call.value
-            }
-            env
-          end
-        end
-        private_class_method :simple
       end
     end