fixes based on code review by @dom96

- For clarity: Changed the unregister if statement to use the in operator instead of
the set intersection operator in ioselectors_epoll.nim and
ioselectors_select.nim.

- Fixed unregister of Event.User case on the Android branch.

lib/pure/ioselects/ioselectors_select.nim

@@ -286,7 +286,7 @@ proc unregister*[T](s: Selector[T], fd: SocketHandle|int) =
   s.withSelectLock():
     let fd = fd.SocketHandle
     var pkey = s.getKey(fd)
-    if pkey.events * {Event.Read, Event.User} != {}:
+    if Event.Read in pkey.events or Event.User in pkey.events:
       IOFD_CLR(fd, addr s.rSet)
       dec(s.count)
     if Event.Write in pkey.events:
@@ -462,4 +462,4 @@ template withData*[T](s: Selector[T], fd: SocketHandle|int, value,
 
 
 proc getFd*[T](s: Selector[T]): int =
-  return -1
+  return -1