The cybersecurity chief for the government’s human resources office resigned on Monday, just two days before she was scheduled to testify to Congress on last year’s massive breach of federal personnel data. Donna K. Seymour, the chief information officer for the Office of Personnel Management, announced her retirement in a letter to colleagues. “It is in the agency’s best interest that my presence does not distract from the great work this team does every single day,” the letter said. She was scheduled to appear Wednesday at a House Oversight and Government Reform Committee hearing. Committee chairman, Republican Utah Rep. Jason Chaffetz, called her resignation “necessary and long overdue.” The agency has acknowledged that personal records for as many as many as 21.5 million people were stolen in attacks on its networks.