Remove UserInaccesible from SetterAccess

`__setter_access` is similar to `_custom` in that this name isn't
actually used when printing. So even though it's double underscored, it
should still be user accessible.

Author: bnbarham

gyb_syntax_support/AttributeKinds.py

@@ -817,7 +817,6 @@ def __init__(self, name, swift_name=None):
     ContextualDeclAttributeAlias('open', 'AccessControl'),
     DeclAttribute('__setter_access', 'SetterAccess',
                   OnVar,  OnSubscript,
-                  UserInaccessible,
                   DeclModifier,  RejectByParser,
                   NotSerialized,
                   ABIStableToAdd,  ABIStableToRemove,  APIStableToAdd,  APIStableToRemove,