remove redundant ports. A comment that I left in the code at the
last commit asked if it was necessary to call efAddNodes and
efAddConns recursively. An example came up in which the answer
is apparently "yes". These routines have been replaced by
efFlatNodes(), which appears to solve the problem. There is now
a question of whether efFlatNodesDeviceless() does anything, and
should its main behavior (to flag deviceless subcircuits) be
folded into efFlatNodes.