openflow_input: remove experimenter OXM header

We expect extensions to use the OXM class.
diff --git a/openflow_input/standard-1.2 b/openflow_input/standard-1.2
index 50bb042..4650e06 100644
--- a/openflow_input/standard-1.2
+++ b/openflow_input/standard-1.2
@@ -604,12 +604,6 @@
     list(of_oxm_t) oxm_list;
 };
 
-struct of_oxm_experimenter_header {
-    uint32_t oxm_header;
-    uint32_t experimenter;
-    of_octets_t data;
-};
-
 struct of_action_output {
     uint16_t type == 0;
     uint16_t len;
diff --git a/openflow_input/standard-1.3 b/openflow_input/standard-1.3
index bc6c524..ccef4db 100644
--- a/openflow_input/standard-1.3
+++ b/openflow_input/standard-1.3
@@ -728,12 +728,6 @@
     list(of_oxm_t) oxm_list;
 };
 
-struct of_oxm_experimenter_header {
-    uint32_t oxm_header;
-    uint32_t experimenter;
-    of_octets_t data;
-};
-
 // This looks like an action header, but is standalone.  See 
 // ofp_table_features_prop_actions
 struct of_action_id {