Leave use-cases out of WBE developer documentation
Leave use-cases out of WBE developer documentation

It doesn't seem appropriate anymore to include the
use-cases for the worker engine in developer documentation
since that information should be placed elsewhere (as its
not especially relevant to developers).

Change-Id: I7eae79bd630572d0c045a2561f2f36bdcf14aaf4

openstack/taskflow,jimbobhickville/taskflow,openstack/taskflow,jimbobhickville/taskflow,pombredanne/taskflow-1,junneyang/taskflow,junneyang/taskflow,pombredanne/taskflow-1