RFC/Ada: removal of $(ADAC) support

[Laurent GUERBY]

Hi, now that we have an official FSF release
with Ada included (and soon a second one), I
propose we drop support for older versions
not supporting C and Ada with the same driver in 3.4
(this is achived by the ADAC Makefile variable with 3.2 and 3.3).

This will limit the amount of variation in the Ada build 
path and remove some configure/Makefile complexity.

Any objection?

Laurent