Make remove more explicit

There was some concern in fixing hub.remove for secondary listeners
because tests seemed to rely on the implicit robustness of hub.remove
when a listener wasn't being tracked.

It was discovered that socket errors can bubble up in poll and select
hubs which result in all listeners being removed for that fileno before
the listener was alerted (which would then *also* triggered a remove).

Rather than having remove be robust to being called twice this change
makes it be called only once.

eventlet/hubs/hub.py

@@ -225,23 +225,19 @@ def remove(self, listener):
 
         fileno = listener.fileno
         evtype = listener.evtype
-        if listener is self.listeners[evtype].get(fileno):
-            self.listeners[evtype].pop(fileno, None)
+        if listener is self.listeners[evtype][fileno]:
+            del self.listeners[evtype][fileno]
             # migrate a secondary listener to be the primary listener
             if fileno in self.secondaries[evtype]:
-                sec = self.secondaries[evtype].get(fileno, None)
-                if not sec:
-                    return
-                self.listeners[evtype][fileno] = sec.pop(0)
+                sec = self.secondaries[evtype][fileno]
+                if sec:
+                    self.listeners[evtype][fileno] = sec.pop(0)
                 if not sec:
                     del self.secondaries[evtype][fileno]
         else:
-            sec = [l for l in self.secondaries[evtype].get(fileno, [])
-                   if l is not listener]
-            if sec:
-                self.secondaries[evtype][fileno] = sec
-            else:
-                self.secondaries[evtype].pop(fileno, None)
+            self.secondaries[evtype][fileno].remove(listener)
+            if not self.secondaries[evtype][fileno]:
+                del self.secondaries[evtype][fileno]
 
     def mark_as_reopened(self, fileno):
         """ If a file descriptor is returned by the OS as the result of some
@@ -255,16 +251,23 @@ def mark_as_reopened(self, fileno):
     def remove_descriptor(self, fileno):
         """ Completely remove all listeners for this fileno.  For internal use
         only."""
+        # gather any listeners we have
         listeners = []
-        listeners.append(self.listeners[READ].pop(fileno, noop))
-        listeners.append(self.listeners[WRITE].pop(fileno, noop))
-        listeners.extend(self.secondaries[READ].pop(fileno, ()))
-        listeners.extend(self.secondaries[WRITE].pop(fileno, ()))
+        listeners.append(self.listeners[READ].get(fileno, noop))
+        listeners.append(self.listeners[WRITE].get(fileno, noop))
+        listeners.extend(self.secondaries[READ].get(fileno, ()))
+        listeners.extend(self.secondaries[WRITE].get(fileno, ()))
         for listener in listeners:
             try:
+                # listener.cb may want to remove(listener)
                 listener.cb(fileno)
             except Exception:
                 self.squelch_generic_exception(sys.exc_info())
+        # NOW this fileno is now dead to all
+        self.listeners[READ].pop(fileno, None)
+        self.listeners[WRITE].pop(fileno, None)
+        self.secondaries[READ].pop(fileno, None)
+        self.secondaries[WRITE].pop(fileno, None)
 
     def close_one(self):
         """ Triggered from the main run loop. If a listener's underlying FD was