BUG/MAJOR: queue/threads: make pendconn_redistribute not lock the server

BUG/MAJOR: queue/threads: make pendconn_redistribute not lock the server

Since commit 3ff577e ("MAJOR: server: make server state changes
synchronous again"), srv_update_status() is called with the server
lock held. It calls (among others) pendconn_redistribute() which used
to take this lock, causing CPU loops by default, or crashes if build
with -DDEBUG_THREAD. Since this function is not called from any other
place anymore, it doesn't require the lock on its own so let's simply
drop it from there.

No backport is needed, this is 1.9-specific.