Fix mouse-key input with ncurses6 in terminals without basic X10 mouse
support, at the cost of breaking it with ncurses5. See discussion in
https://midnight-commander.org/ticket/4144 .

--- a/lib/tty/key.c
+++ b/lib/tty/key.c
@@ -2124,8 +2124,7 @@
         gboolean extended = c == MCKEY_EXTENDED_MOUSE;
 
 #ifdef KEY_MOUSE
-        extended = extended || (c == KEY_MOUSE && xmouse_seq == NULL
-                                && xmouse_extended_seq != NULL);
+        extended = extended || (c == KEY_MOUSE && xmouse_extended_seq != NULL);
 #endif /* KEY_MOUSE */
 
         xmouse_get_event (event, extended);