ipc: strip machinery no peer uses; keep client state in one Keyreq

ipc.c: an AF_UNIX nonblocking connect completes at once or fails with
EAGAIN, so the EINPROGRESS/poll/SO_ERROR path and the fcntl juggling
were dead; the deadline plumbing checked a clock that cannot fail and
re-tested the deadline before every transfer although only waitfd
blocks; readfield's truncation and discard loop served the unit test,
since every caller owns char[Ipcfieldmax+1]; NULL-argument checks on
in-tree encoders are gone (peer validation stays). The primary key frame
is Ipckey, not 'legacy'; ipckeysym names the keysym mapping.

srv.c: the per-connection capability and caret already lived in the
persistent Keyreq; the mirror locals and 'negotiated' flag guarded a
protocol rule no client relied on. proccreate never fails in libthread.

gtk: focus-out no longer round-trips a reset before closing the socket
that releases the engine; the caret dedup compares the packed frame;
srvconnect's preedit no-ops and the insimple flag are gone.

tests/gtk_live_test.c

@@ -204,7 +204,7 @@ request(Server *s, int fd)
 		e.type = Ecaret;
 		record(s, &e);
 		return 1;
-	case Ipclegacy:
+	case Ipckey:
 		ipcunpackreq(buf, &want, &mod, &key);
 		e.want = want;
 		e.key = key;
@@ -854,9 +854,8 @@ main(int argc, char **argv)
 	first = eventcount(&srv);
 	closes = closecount(&srv);
 	gtk_im_context_focus_out(ctx);
-	Check(waitcount(&srv, first + 1) && getevent(&srv, first).type == Ereset,
-		"focus-out reset missing");
 	Check(waitclose(&srv, closes + 1), "focus-out did not close connection");
+	Check(eventcount(&srv) == first, "focus-out sent a request before closing");
 	Check(strcmp(log.event, "CE") == 0, "focus-out clear order was %s", log.event);
 
 	/* Dispose is repeatable, closes the connection, and emits no preedit. */