Since the sdl to target tree move, the main thread cannot be removed anymore,

since it's now the default thread which is implicitely created by starting the sim.

This caused a segfault that r26283 tried to fix. Revert r26283 and protect
the main thread from being removed.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26315 a1c6a512-1295-4272-9138-f99709370657

firmware/target/hosted/sdl/button-sdl.c

@@ -176,7 +176,6 @@ void gui_message_loop(void)
             case SDL_QUIT:
             {
                 sim_exit_irq_handler();
-                SDL_Quit();
                 exit(EXIT_SUCCESS);
                 break;
             }