dcache-qos: remove singleton service configuration

Motivation:

As originally conceived, the qos service suite
could be run as a single component.

The added maintenance overhead for configuration
duplication and testing is not really justified;
not much is gained by doing this and I imagine
the option has not yet even been tried.

Modification:

Deprecate/eliminate the option.

Result:

Less to maintain and test.

Target:  master
Patch: https://rb.dcache.org/r/14053/
Requires-notes: yes
Requires-book: yes (included)
Acked-by: Tigran

docs/TheBook/src/main/markdown/config-qos-engine.md

@@ -146,6 +146,10 @@ With respect to the example scanner domain: the scanner communicates directly wi
 so `chimera.db.host` should be set explicitly if it is not running on the same host
 as the database.
 
+> NOTE:  As of dCache 9.2, the singleton configuration has been removed.  Each of the
+> separate services can be run together in one domain or in separate domains, but it is
+> no longer possible to run the entire QoS component suite as a single service.
+
 ### Memory requirements
 
 While it is possible to run QoS in the same domain as other services,