Tunis, July 31 (IANS) The Tunisian army chief,Mohamed Salah Hamdi , has stepped down from his post as the highest commander, the defence ministry confirmed Wednesday. Hamdi had presented his letter of resignation July 23, less than a week after 15 soldiers were killed by militants along the Algerian border. He was leaving for "personal" reasons, Xinhua quoted Defence Minister Ghazi Jeribi as saying