INS: use an accessor method on the state

Publically exposing the Nav structure was bad design.
INS: Remove old 16 state version

Not used and previous change broke it.  It will be in history
if needed.
INS: get rid of unused Nav structure
INS: make functions that should be static

This code is quite old and was committed before our standards were
so high.
Merge pull request #531 from peabody124/ins_get_state

INS cleanups