Deprecate - Class#superclass_delegating_accessor

```ruby
class TestClass
  superclass_delegating_accessor :test_attribute
end

# Before
TestClass.private_methods.include?(:_test_attribute) # => false
TestClass.private_methods.include?(:_test_attribute=) # => false

# After
TestClass.private_methods.include?(:_test_attribute) # => true
TestClass.private_methods.include?(:_test_attribute=) # => true
```