remove the $name parameter that add_attribute doesn't take

thanks to pheix++ on irc for the tip

Author: timo

doc/Type/Metamodel/AttributeContainer.pod6

@@ -13,7 +13,7 @@ attributes is implemented by this role.
 
 =head2 method add_attribute
 
-    method add_attribute(Metamodel::AttributeContainer: $obj, $name, $attribute)
+    method add_attribute(Metamodel::AttributeContainer: $obj, $attribute)
 
 Adds an attribute. C<$attribute> must be an object that supports the
 methods C<name>,  C<type> and C<package>, which are called without arguments.