Morgan Stanley’s two top investment bankers are resigning from the securities firm on Wednesday, the most painful departures to hit the firm since a management shakeup late last month.Joseph Perella, Morgan’s investment banking chairman and company vice chairman and one of the best-known bankers on Wall Street, is resigning after 12 years at the firm. Tarek ‘‘Terry’’ Abdel-Meguid, Perella’s deputy and the head of investment banking, is also quitting, a person familiar with the situation said.
