PM / core: Drop legacy class suspend/resume operations

There are no classes using the legacy suspend/resume operations in
the tree any more, so drop these operations and update the code
referring to them accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>