include/sysemu/sysemu.h: Remove usused variable no_quit

The no_quit variable has been removed in commit 7878271 ("vl: drop
no_quit variable"), so let's remove the extern declaration in the header
now, too.

Fixes: 7878271 ("vl: drop no_quit variable")
Message-Id: <20200108192402.19672-1-thuth@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

include/sysemu/sysemu.h

@@ -44,7 +44,6 @@ extern int alt_grab;
 extern int ctrl_grab;
 extern int cursor_hide;
 extern int graphic_rotate;
-extern int no_quit;
 extern int no_shutdown;
 extern int old_param;
 extern int boot_menu;