By Sinead Cruise LONDON (Reuters) -Citigroup is overhauling the leadership of one of the teams linked to a ‘flash crash’ that sent European stock markets tumbling this month, three sources told Reuters. Citi is looking to name a new Head of Forward Trading in its Delta One operations based at its European headquarters in London, a job vacancy posted on professional networking site LinkedIn shows. Ali Omari, who was EMEA Head of Delta One Forwards and Sectors, has left the U.S. bank in a decision unrelated to the event, two people with knowledge of his departure, who declined to be named, said….