The Philadelphia Episcopal Cathedral, a decade after withering criticism of what many viewed as a destructive renovation of its own ornate Victorian interior, is planning to demolish two historically certified brownstone structures in the 3800 block of Chestnut Street to make way for a 25-story apartment tower. The project, which goes before the Philadelphia Historical Commission Friday, would obliterate the cathedral’s parish houses, designed by the noted ecclesiastical architect Charles M. Burns, and connect the proposed tower and administrative offices to the church itself via glass-enclosed walkways cut into the cathedral’s façade.