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/vfs101.c

@@ -17,14 +17,14 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#define FP_COMPONENT "vfs101"
+
+#include "fp_internal.h"
+
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
 
-#define FP_COMPONENT "vfs101"
-
-#include <fp_internal.h>
-
 #include "driver_ids.h"
 
 /* Input-Output usb endpoint */