[BUG] ev_sepoll: closed file descriptors could persist in the spec list

[BUG] ev_sepoll: closed file descriptors could persist in the spec list

If __fd_clo() was called on a file descriptor which was previously
disabled, it was not removed from the spec list. This apparently
could not happen on previous code because the TCP states prevented
this, but now it happens regularly. The effects are spec entries
stuck populated, leading to busy loops.

(cherry picked from commit 7a52a5c4680477272b2f34eaf5896b85746e6fd6)
(cherry picked from commit 116f4105d4fc6fbd8f2d0a139f691973332176de)