The corresponding WorkerT continues to exist, but is removed from all
WorkerManagers so that it does not get called for any transitions. The
deleted modules are removed from PathsAndConsumesOfModules.

Allow worker_ to be nullptr in UnscheduledProductResolver, can happen
if a module is deleted early.

The Worker::description() returns now nullptr if module was deleted.
The description() is not expected to be called when the module is
deleted, so this change is mostly a safety check in the hope of
getting a segfault if the nullptr is accessed.

Need to pass module label and process name for consumes of products of
parent (sub)process(es).

…l/stream/limited/one tests

…ast one in the chain to a Path

Without a scheduled module consuming their output all modules would be deleted.

…ss unit test

…duleTimer

From David Dagenhart:
> It is not at all obvious looking at it, but this change just
> coincidentally happens to give the execution order 'a' then 'c' then
> 'b'. Since the purpose of the test is to demonstrate the Framework
> is forcing that execution order we should probably perturb this in
> some way so it isn't just doing it by accident. Renaming 'a' to 'd'
> seems to do the trick.