bluez5_utils: correct the experimental option text

In BlueZ 5.44 the --enable-experimental configure option only controls the
build of the Nokia OBEX PC Suite plugin. Correct the option prompt and help
text.

Cc: Marcin Bis <marcin@bis.org.pl>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>