adapter: Remove experimental flag for PowerState

Now that the feature has been tested, that the API is deemed adequate
and the reliability sufficient.

[Emil Velikov]
The feature has landed in Sept 2022, with inclinations that "we might
switch it to stable in the next release", back in Nov 2022.

Today - a bit over 1 year later -  various distributions (Fedora, Gentoo
and by extension their derivatives) are carrying this patch. I think we
can say we're reasonably stable and can merge it upstream.

src/adapter.c

@@ -3914,8 +3914,7 @@ static const GDBusPropertyTable adapter_properties[] = {
 	{ "Alias", "s", property_get_alias, property_set_alias },
 	{ "Class", "u", property_get_class },
 	{ "Powered", "b", property_get_powered, property_set_powered },
-	{ "PowerState", "s", property_get_power_state, NULL, NULL,
-			     G_DBUS_PROPERTY_FLAG_EXPERIMENTAL },
+	{ "PowerState", "s", property_get_power_state },
 	{ "Discoverable", "b", property_get_discoverable,
 					property_set_discoverable },
 	{ "DiscoverableTimeout", "u", property_get_discoverable_timeout,