iochannel: remove fd from poll() when we don't care from events

This should make it unlikely that we loop on SIGHUP indefinitely.

Also, this makes it possible for callbacks not to process all events and
still not busy loop.

src/pulsecore/iochannel.h

@@ -38,11 +38,6 @@
    the channel a callback function is called. It is safe to destroy
    the calling iochannel object from the callback */
 
-/* When pa_iochannel_is_readable() returns non-zero, the user has to
- * call this function in a loop until it is no longer set or EOF
- * reached. Otherwise strange things may happen when an EOF is
- * reached. */
-
 typedef struct pa_iochannel pa_iochannel;
 
 /* Create a new IO channel for the specified file descriptors for