cleanup: general removal of TODO (and similar) comments

They tend to never get updated anyway so they're frequently inaccurate
and we never go back to revisit them anyway. We document issues to work
on properly in KNOWN_BUGS and TODO instead.

lib/ftp.c

@@ -3659,7 +3659,7 @@ static CURLcode ftp_do_more(struct connectdata *conn, int *completep)
   if(!conn->bits.tcpconnect[SECONDARYSOCKET]) {
     if(conn->tunnel_state[SECONDARYSOCKET] == TUNNEL_CONNECT) {
       /* As we're in TUNNEL_CONNECT state now, we know the proxy name and port
-         aren't used so we blank their arguments. TODO: make this nicer */
+         aren't used so we blank their arguments. */
       result = Curl_proxyCONNECT(conn, SECONDARYSOCKET, NULL, 0, FALSE);
 
       return result;