Remove the AttrBuilder form of the Attribute::get creators.

The AttrBuilder is for building a collection of attributes. The Attribute object
holds only one attribute. So it's not really useful for the Attribute object to
have a creator which takes an AttrBuilder.

This has two fallouts:

1. The AttrBuilder no longer holds its internal attributes in a bit-mask form.
2. The attributes are now ordered alphabetically (hence why the tests have changed).