api,dbus: simplified the Manager API, as we will use the standard ObjectManager

The recent `org.freedesktop.DBus.ObjectManager' standard API defines a common
way to handle a list of objects in the interface. It allows getting all objects,
interfaces and properties in a single method call.

See:
http://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-objectmanager

new/org.freedesktop.ModemManager1.xml

@@ -5,18 +5,6 @@
 
     <!-- METHODS -->
 
-    <method name="GetDevices">
-      <tp:docstring>
-        Get the list of modems known to ModemManager.
-      </tp:docstring>
-      <annotation name="org.freedesktop.DBus.GLib.CSymbol" value="impl_manager_get_devices"/>
-      <arg name="devices" type="ao" direction="out">
-	<tp:docstring>
-	  List of object paths of modem devices known to the system.
-	</tp:docstring>
-      </arg>
-    </method>
-
     <method name="ScanDevices">
       <tp:docstring>
         Start a new scan for connected modem devices.
@@ -37,35 +25,5 @@
       </arg>
     </method>
 
-    <signal name="ModemAdded">
-      <tp:docstring>
-	A modem was added to the system.
-      </tp:docstring>
-      <arg name="device" type="o">
-	<tp:docstring>
-	  The object path of the newly added modem.
-	</tp:docstring>
-      </arg>
-    </signal>
-
-    <signal name="ModemRemoved">
-      <tp:docstring>
-	A modem was removed from the system, and is no longer available.
-      </tp:docstring>
-      <arg name="device" type="o">
-	<tp:docstring>
-	  The object path of the modem that was just removed.
-	</tp:docstring>
-      </arg>
-    </signal>
-
-    <!-- PROPERTIES -->
-
-    <property name="Modems" type="ao" access="read">
-      <tp:docstring>
-        Array of object paths of all modems known to ModemManager.
-      </tp:docstring>
-    </property>
-
   </interface>
 </node>