Fixed comm_close handling in deferred reads. The code was expecting old-style

Fixed comm_close handling in deferred reads. The code was expecting old-style
comm_remove_close_handler call to work if the close handler has not been
dialed yet. We now store a new-style callback so that we can reliably cancel
the close hander call.

Removed all methods from CommRead except for constructors. Apparently,
they were all unused and most were not even defined.