engine: look dictionaries up synchronously

The dictionary thread ran in imthread's own proc, so a lookup could
only start once the engine blocked, and it was a trie probe anyway; the
emoji and Hanja searches already called dictlookup directly. The
request/result channels, sequence numbers, staleness checks and the
second draw per Japanese key are gone; dictqjp fills the candidates
in place. Emit.dict and Lang.dictq only ever triggered lookups for
Vietnamese, which has no dictionary. dictlookup(Lang*, key, out, max)
returns the count. The Hanja lookup no longer pre-checks for a single
syllable; a reading either has an entry or it does not.

main.c

@@ -3,8 +3,6 @@
 
 Channel *drawc;
 Channel *keyc;
-Channel *dictreqc;
-Channel *dictresc;
 
 void
 usage(void)
@@ -56,8 +54,6 @@ threadmain(int argc, char **argv)
 
 	drawc = chancreate(sizeof(Drawcmd), 4);
 	keyc = chancreate(sizeof(Keyreq), 0);
-	dictreqc = chancreate(sizeof(Dictreq), 4);
-	dictresc = chancreate(sizeof(Dictres), 0);
 	langinit(argv[1]);
 	srvinit();
 	proccreate(drawthread, nil, 16384);
@@ -66,6 +62,5 @@ threadmain(int argc, char **argv)
 	display = getenv("DISPLAY");
 	if(display != nil && display[0] != '\0')
 		proccreate(ximthread, nil, 32768);
-	threadcreate(dictthread, nil, 16384);
 	imthread(nil);
 }