By Se Young Lee SEOUL (Reuters) – Nearly 200 management-level executives at Samsung Electronics Co Ltds mobile division voluntarily returned a quarter of their first-half bonuses, a source with direct knowledge of the matter said on Friday, with the company poised to post its worst quarterly profit in two years. Samsung Electronics, the worlds biggest smartphone maker, estimated earlier this month that its operating profit reached 7.2 trillion won ($7 billion) for April-June, far below most analysts forecasts. A Samsung Electronics spokeswoman declined to comment. …