Rip out old hidden implementation.

src/metamodel/ClassHOW.pir

@@ -56,7 +56,6 @@ calls on it.
     # Extra attributes for interface consistency and compositiony stuff.
     addattribute $P0, '$!attributes'
     addattribute $P0, '$!hides'
-    addattribute $P0, '$!hidden'
     addattribute $P0, '$!composees'
     addattribute $P0, '$!done'
     addattribute $P0, '$!ver'
@@ -790,24 +789,6 @@ Accessor for hides property.
 .end
 
 
-=item hidden
-
-Accessor for hidden property.
-
-=cut
-
-.sub 'hidden' :method
-    .local pmc obj
-    $P0 = getattribute self, '$!hidden'
-    unless null $P0 goto done
-    $P0 = get_hll_global ['Bool'], 'False'
-    $P0 = new ['Perl6Scalar'], $P0
-    setattribute self, '$!hidden', $P0
-  done:
-    .return ($P0)
-.end
-
-
 =item new_class(name [, 'parent'=>parentclass] [, 'attr'=>attr] [, 'hll'=>hll] [, 'does_role'=>r)
 
 Override of new_class from P6metaclass that handles attributes through the