event/SocketMonitor: don't close the socket automatically

Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

src/event/Loop.cxx

@@ -42,9 +42,6 @@ EventLoop::~EventLoop()
 {
 	assert(idle.empty());
 	assert(timers.empty());
-
-	/* avoid closing the WakeFD twice */
-	SocketMonitor::Steal();
 }
 
 void