lib: Use GLib and libusb directly for debug output

Use GLib internally to output debug information, and tell about
libusb's LIBUSB_DEBUG envvar for libusb debug.

fp_set_debug() is now a no-op.

https://bugs.freedesktop.org/show_bug.cgi?id=106552

libfprint/drivers/vcom5s.c

@@ -19,6 +19,8 @@
 
 #define FP_COMPONENT "vcom5s"
 
+#include "fp_internal.h"
+
 /* TODO:
  * calibration?
  * image size: windows gets 300x300 through vpas enrollment util?
@@ -32,8 +34,6 @@
 #include <glib.h>
 #include <libusb.h>
 
-#include <fp_internal.h>
-
 #include "driver_ids.h"
 
 #define CTRL_IN 0xc0