Deprecate callback privilege from OpenBMC

Deprecate callback privilege from OpenBMC system, as this OpenBMC
doesn't support callback, and this privilege is not applicable
anymore. No-access entry is listed (Users not belonging to any
privilege level must be reported as NoAccess from IPMI & REDFISH
point of it.

Change-Id: I5de6d00795cd5b5fe4f72eb469d62db00bb74070
Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
diff --git a/architecture/user_management.md b/architecture/user_management.md
index ac8e8c2..d679f1e 100644
--- a/architecture/user_management.md
+++ b/architecture/user_management.md
@@ -62,7 +62,7 @@
 |1     | admin           | Users are allowed to configure all OpenBMC (including user-management, network and all configurations). Users will have full administrative access.|
 |2     | operator        | Users are allowed to view and control basic operations. This includes reboot of the host, etc. But users are not allowed to change other configuration like user, network, etc.|
 |3     | user            | Users only have read access and can't change any behavior of the system.|
-|4     | callback        | Lowest privilege level, only allowed to initiate IPMI 2.0 specific callbacks.|
+|4     | no-access       | Users having empty or no privilege will be reported as no-access, from IPMI & REDFISH point of it.|
 
 ## Common User Manager - D-Bus API (phosphor-user-manager)
 User Manager service exposes D-Bus methods for user-management operations.