[hooks/security] Streamline attributes default permission check.
The current default permission on attributes delegates the check to
the entity permission update policy.
Since this is already checked it can be skipped.
The equality comparison will work, even with a deserialized schema,
because the default update perm is::
('managers', ERQLExpression(Any X WHERE U has_update_permission X, X eid %(x)s, U eid %(u)s))
which will always be deserialized in this order (groups first).
However this is a slight semantic change: entity type level 'update'
permissions can now be effectively used to encode update-time rules if
the default attribute permissions are used (before this change, the
'update' rules at entity type level were fired at creation time).
Closes #2930861.