Use atexit() instead of defining a custom exit_program() interface.

cmdutils.h

@@ -400,15 +400,9 @@ int64_t guess_correct_pts(PtsCorrectionContext *ctx, int64_t pts, int64_t dts);
 FILE *get_preset_file(char *filename, size_t filename_size,
                       const char *preset_name, int is_path, const char *codec_name);
 
-/**
- * Do all the necessary cleanup and abort.
- * This function is implemented in the avtools, not cmdutils.
- */
-av_noreturn void exit_program(int ret);
-
 /**
  * Realloc array to hold new_size elements of elem_size.
- * Calls exit_program() on failure.
+ * Calls exit() on failure.
  *
  * @param elem_size size in bytes of each element
  * @param size new element count will be written here