Change archive behavior so that task details / artifacts are automatically purged

[davidahouse]

Instead of leaving this job up to an external script, we should be purging task details / artifacts whenever the build is archived. So for this change we need to do the following:

• add a delete of taskDetails and artifacts to the retention handler process
• remove the APIs around finding a build with task details and removing task details

Also we might need to make a decision about existing archived taskDetails and how best to deal with it. Depending on the implementation we take above, we might can do both at once (for example we could simply delete any taskDetails that are associated with an archived build).