worker attribute of /subsystem=remoting should not have a default value

This attribute is a reference to a capability from the IO subsystem, and thus should not have a magic default value.
The proposed fix for WFCORE-6472 applies a default value only for server processes.
Dropping the default value entirely will mean making this attribute required for server processes. However, this will break any legacy CLI scripts (and unversioned YAML config) that previously relied on this default.