profiling doesn't work in do_admb

example from vignette doesn't work now! (`profpars` not found)

as reported by Oliver Stirrup on r-sig-mixed-models

Start by reproducing the profiling example from the vignette through do_admb and record where profpars is expected but not found. Trace the profiling-related entry point and determine what behavior the example should have; done means the vignette example runs successfully without the profpars error.

Written by the indexing model from the issue text.