system_api: cros-disks: remove ExperimentalFeaturesEnabled property

The 'ExperimentalFeaturesEnabled' property has been removed for a long
time.

BUG=None
TEST=Remote trybot builds.

Change-Id: Ia5fe77e563bb9f0840c8bd3b55023ed3add25e93
Reviewed-on: https://chromium-review.googlesource.com/486261
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/dbus/cros-disks/dbus-constants.h b/dbus/cros-disks/dbus-constants.h
index c58af38..392337d 100644
--- a/dbus/cros-disks/dbus-constants.h
+++ b/dbus/cros-disks/dbus-constants.h
@@ -46,7 +46,6 @@
 const char kDeviceSize[] = "DeviceSize";
 const char kDriveIsRotational[] = "DriveIsRotational";
 const char kDriveModel[] = "DriveModel";
-const char kExperimentalFeaturesEnabled[] = "ExperimentalFeaturesEnabled";
 const char kIdLabel[] = "IdLabel";
 const char kIdUuid[] = "IdUuid";
 const char kVendorId[] = "VendorId";