By Euan Rocha TORONTO (Reuters) – BlackBerry Ltd is abandoning a plan to sell itself and will raise about $1 billion from its largest shareholder and other institutional investors as it tries yet again to revive its fortunes. The smartphone maker said on Monday that Chief Executive Officer Thorsten Heins would leave in about two weeks, as soon as the private placement of convertible debentures closes. His interim successor will be John Chen, the former CEO of Sybase, a database software company that SAP AG acquired in 2010. Chen, who will also be BlackBerrys new executive chairman, joined private equity group Silver Lake as senior adviser a year ago.