Remove deprecation warning without a deprecator

The initial deprecation was introduced in 6.1:
bbfab0b

The configuration stayed with a deprecation in 7.0 but was not
preserving the behavior: 10bd5e5

This removes the configuration and deprecation.

activejob/lib/active_job/callbacks.rb

@@ -28,9 +28,6 @@ class << self
     end
 
     included do
-      cattr_accessor :skip_after_callbacks_if_terminated, instance_accessor: false, default: false
-      singleton_class.deprecate :skip_after_callbacks_if_terminated, :skip_after_callbacks_if_terminated=
-
       define_callbacks :perform, skip_after_callbacks_if_terminated: true
       define_callbacks :enqueue, skip_after_callbacks_if_terminated: true
     end