shill: remove unused "Networks" property from Device interface

flimflam used to expose a "Networks" property on the
org.chromium.flimflam.Device interface. After shill superseded flamflam,
shill never expose the "Networks" property on the
org.chromium.flimflam.Device interface. There is no use case of such a
property, so this CL simply removes the constant for the "Networks"
property from system_api.

BUG=None
TEST=Remote trybot runs.

Change-Id: Ibaf240c270db1081eb22aff2ad47f28e69ba1e18
Reviewed-on: https://chromium-review.googlesource.com/505189
Commit-Ready: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
diff --git a/dbus/shill/dbus-constants.h b/dbus/shill/dbus-constants.h
index 063d70a..118c7a9 100644
--- a/dbus/shill/dbus-constants.h
+++ b/dbus/shill/dbus-constants.h
@@ -164,7 +164,6 @@
 // Flimflam Device property names.
 const char kScanningProperty[] = "Scanning";
 const char kPoweredProperty[] = "Powered";
-const char kNetworksProperty[] = "Networks";
 const char kScanIntervalProperty[] = "ScanInterval";
 const char kBgscanMethodProperty[] = "BgscanMethod";
 const char kBgscanShortIntervalProperty[] = "BgscanShortInterval";