Revert "qdev: Add help for device properties"

Revert "qdev: Add help for device properties"

This reverts commit 2ba6edf0dd740166632df80caa85992b20791a68.

The commit has two issues:

* When it runs from the monitor, e.g. "device_add e1000,?", it prints
  to stderr instead of the monitor.

* Help looks to callers just like failed device creation.  This makes
  main() exit unsuccessfully on "-device e1000,?".

We need to do this differently.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>