Remove trailing space from RPL_NAMREPLY

This is disallowed by https://modern.ircdocs.horse/#rplnamreply-353 and
RFC2812; allowed by RFC1459 ambiguous grammar; and only irc2 seems to send
such a trailing space.

sable_ircd/src/utils/channel_names.rs

@@ -51,6 +51,7 @@ pub fn send_channel_names(
         }
         current_line.write_fmt(format_args!("{}{} ", p, n))?;
     }
+    current_line.pop(); // Remove trailing space
     lines.push(current_line);
 
     for line in lines {