xdg-shell: Remove the old unstable version enum and request

As of version 6, the new unstable protocol discovery semantics are
used, so lets remove the enum and request that made up the old one.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>

unstable/xdg-shell/xdg-shell-unstable-v6.xml

@@ -35,16 +35,6 @@
       desktop environments.
     </description>
 
-    <enum name="version">
-      <description summary="latest protocol version">
-	The 'current' member of this enum gives the version of the
-	protocol.  Implementations can compare this to the version
-	they implement using static_assert to ensure the protocol and
-	implementation versions match.
-      </description>
-      <entry name="current" value="5" summary="Always the latest version"/>
-    </enum>
-
     <enum name="error">
       <entry name="role" value="0" summary="given wl_surface has another role"/>
       <entry name="defunct_surfaces" value="1" summary="xdg_shell was destroyed before children"/>
@@ -62,17 +52,6 @@
       </description>
     </request>
 
-    <request name="use_unstable_version">
-      <description summary="enable use of this unstable version">
-	Negotiate the unstable version of the interface.  This
-	mechanism is in place to ensure client and server agree on the
-	unstable versions of the protocol that they speak or exit
-	cleanly if they don't agree.  This request will go away once
-	the xdg-shell protocol is stable.
-      </description>
-      <arg name="version" type="int"/>
-    </request>
-
     <request name="get_xdg_surface">
       <description summary="create a shell surface from a surface">
 	This creates an xdg_surface for the given surface and gives it the