Drop confusing splash cmdline and --enable-progress configure option

This patch reverts back to the progress/status behavior of Finit < v3.0
because this is what most users expect, including the maintainer.  The
resulting code and configure script is a lot simpler to understand and
maintain:

- No more --enable-progress or --enable-progress-classic configure
  flags.  Instead a progress_style variable in helpers.c that can
  be changed at compile time for those that really need it.
- No more 'splash' kernel commnand line option.  This turned out to
  be *very* confusing to many users who believed it was some sort of
  graphical splash screen à la Plymouth.

Also, when Finit debug is enabled we now have a global 'debug' flag
which now alo controls if klogctl() should be called to prevent the
kernel logs to the console or not.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/helpers.h

@@ -55,6 +55,7 @@ void    console_init    (void);
 ssize_t cprintf         (const char *fmt, ...);
 
 char   *strip_line      (char *line);
+void    show_progress   (int onoff);
 
 int     getty           (char *tty, speed_t speed, char *term, char *user);
 int     sh              (char *tty);