fish_key_reader: stop emitting \n for ctrl-j

I guess it's nice to know that these two are the same but that info is not
needed here, it just adds confusion. The user must have pressed ctrl-j if
we get here, so echo that back.

See the parent commit.

src/key.rs

@@ -421,7 +421,6 @@ fn ctrl_to_symbol(buf: &mut WString, c: char) {
     let c = u8::try_from(c).unwrap();
     let symbolic_name = match c {
         9 => L!("\\t"),
-        10 => L!("\\n"),
         13 => L!("\\r"),
         27 => L!("\\e"),
         _ => return sprintf!(=> buf, "\\x%02x", c),