The Social Security Administration did not fully assess the impact of a major internal overhaul last June, which eliminated the chief information office and reassigned its functions, according to testimony from a Government Accountability Office official.   At the time, most of the responsibilities for managing information technology and the IT budget were reassigned to SSA’s Office of Systems. Two months later, then CIO Frank Baitman resigned. Kelly Croft, deputy commissioner for systems, assumed the CIO duties and oversight of those IT workers.   SSA Commissioner Michael Astrue said the effort would increase efficiency, but SSA did not develop a management plan…