and is wrong into two ways: the search stack is generally not a
path, and does not run until the end of the STL container.
Remove it.
* src/tgbaalgos/tarjan_on_fly.cc, src/tgbaalgos/tarjan_on_fly.hh
(tarjan_on_fly): Do not inherit from the emptiness_search class,
because the check method will no longer return a counter example.
(tarjan_on_fly::check): Return only a boolean.
(tarjan_on_fly::build_counter): Delete.
* src/tgbatest/ltl2tgba.cc: Adjust.