script: fix unused variable in textbox.

When creating a config file, the output says scripts/kconfig/lxdialog/textbox.c: In function ‘print_line’:
scripts/kconfig/lxdialog/textbox.c:323:9: warning: variable ‘x’ set but not used [-Wunused-but-set-variable]
  int y, x;
         ^
scripts/kconfig/lxdialog/textbox.c:323:6: warning: variable ‘y’ set but not used [-Wunused-but-set-variable]
  int y, x;
      ^

This is just a warning because of a variable which is not used. Remove it so we don't get the warning.
Signed-off-by: Gianmarco Rengucci <rengucci.gianmarco@gmail.com>