Remove STATUSTEXT_LONG (unused)

A better solution has been proposed and merged in mavlink#1295.

message_definitions/v1.0/common.xml

@@ -5279,11 +5279,6 @@
       <extensions/>
       <field type="float[58]" name="data">data</field>
     </message>
-    <message id="365" name="STATUSTEXT_LONG">
-      <description>Status text message (use only for important status and error messages). The full message payload can be used for status text, but we recommend that updates be kept concise. Note: The message is intended as a less restrictive replacement for STATUSTEXT.</description>
-      <field type="uint8_t" name="severity" enum="MAV_SEVERITY">Severity of status. Relies on the definitions within RFC-5424.</field>
-      <field type="char[254]" name="text">Status text message, without null termination character.</field>
-    </message>
     <message id="373" name="GENERATOR_STATUS">
       <wip/>
       <!-- This message is work-in-progress and it can therefore change. It should NOT be used in stable production environments. -->