Alias for attribute causes aliasing method to appear in Attributes section

When defining an alias for an attribute in a class, the aliasing method is incorrectly displayed in the attributes section of the generated documentation.

For example, consider the following code in lib/foo.rb:

class Foo
  attr :bar
  alias baz bar
end

When running rdoc, the documentation for the Foo class shows:

This behavior is misleading, as baz is not a separate attribute but an alias method for bar method (and attribute). It would be beneficial to adjust the documentation generation to prevent alias methods from appearing in the attributes section.

Start with the RDoc behavior described for lib/foo.rb and run rdoc on the example containing attr :bar and alias baz bar. Inspect the generated Foo documentation; done means baz no longer appears in the attributes section while bar remains documented.