interface/Makefile.am: drop test target
interface/Makefile.am: drop test target

This target may have been introduced by mistake in 1157635374
(add extract_interface for constructing interfaces to other languages,
Tue Aug 2 12:58:48 2011 +0200).  It definitely stopped working in
d192deb9ad (add command line options for output language,
Sat Apr 8 05:12:48 2017 +0200).
Remove the target since it does not work and does not seem to serve
any purpose.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

inducer/isl-mirror,PollyLabs/isl,inducer/isl-mirror,PollyLabs/isl,PollyLabs/isl,nicolasvasilache/isl,nicolasvasilache/isl,nicolasvasilache/isl,inducer/isl-mirror,inducer/isl-mirror,nicolasvasilache/isl,Meinersbur/isl,PollyLabs/isl,Meinersbur/isl,nicolasvasilache/isl,tobig/isl,Meinersbur/isl,inducer/isl-mirror,PollyLabs/isl,Meinersbur/isl,tobig/isl,tobig/isl,tobig/isl