bindings: stop supporting <Esc> <Esc> <numeric slash> without NumLock

<Ctrl+numeric slash> does not invoke Go To Line, so it is fitting
that <Esc> <Esc> <numeric slash> does neither.  If some user does
want the double escape plus slash to work, they can use --raw.

(Also, if someone really uses <Esc> <Esc> <numeric slash>, they
probably also type the desired line number on the numeric keypad,
and for that to work they needed to have NumLock engaged, and in
that case the double escape plus slash will work fine.)

(Getting rid of this numeric-slash support makes the three-escapes
case very similar to the one-escape case, allowing the first to be
folded into the latter in the next commit.)

src/winio.c

@@ -1039,10 +1039,8 @@ int parse_kbinput(WINDOW *win)
 					retval = keycode;
 			} else
 				/* Three escapes followed by a non-escape, and more
-				 * codes are waiting: combined control character and
-				 * escape sequence mode.  First interpret the escape
-				 * sequence, then the result as a control sequence. */
-				retval = convert_to_control(parse_escape_sequence(keycode));
+				 * codes are waiting: escape sequence mode. */
+				retval = parse_escape_sequence(keycode);
 			escapes = 0;
 			break;
 	}