shill: cellular: Move Scanning property from capabilities to cellular.

This is a part of an effort to move all exposed DBus properties of shill from
CellularCapability* to Cellular.

BUG=chromium:322747
TEST=(1) Run network_3GScanningProperty
     (2) Check that the ui for network scanning updates correctly on link,
         and lumpy
             (1) During initialization of the modem
             (2) After the user disables/enables the modem.
             (3) When the user initiates a scan from the ui.

Change-Id: I9bfeae70cf54f74a047047a2e091768821ff48b2
Reviewed-on: https://chromium-review.googlesource.com/182250
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
diff --git a/cellular_capability_universal_cdma.cc b/cellular_capability_universal_cdma.cc
index c6cae61..059e98b 100644
--- a/cellular_capability_universal_cdma.cc
+++ b/cellular_capability_universal_cdma.cc
@@ -508,9 +508,11 @@
   // TODO(armansito): Remove once 3GPP is implemented in its own class.
 }
 
-void CellularCapabilityUniversalCDMA::Scan(Error *error,
-                                           const ResultCallback &callback) {
+void CellularCapabilityUniversalCDMA::Scan(
+    Error *error,
+    const ResultStringmapsCallback &callback) {
   // TODO(armansito): Remove once 3GPP is implemented in its own class.
+  OnUnsupportedOperation(__func__, error);
 }
 
 void CellularCapabilityUniversalCDMA::OnSimPathChanged(