Fixes #148.

* spot/twa/twa.hh, spot/twa/twa.cc, spot/kripke/fairkripke.hh,
spot/kripke/fairkripke.cc, spot/ta/tgtaexplicit.hh,
spot/ta/tgtaexplicit.cc, spot/twa/twagraph.hh, spot/twa/twaproduct.hh,
spot/twa/twaproduct.cc, spot/twaalgos/stutter.cc, spot/twa/taatgba.hh,
spot/twa/taatgba.cc: Remove the method.
* spot/taalgos/tgba2ta.cc: Emulate it with a simple loop.
* NEWS: Mention the removal.