qmp-commands: remove query-qmp-schema from txt

It's better described in the schema already.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

docs/qmp-commands.txt

@@ -107,15 +107,3 @@ Example:
 <- { "return": {} }
 
 Note: This command must be issued before issuing any other command.
-
-3. Query Commands
-=================
-
-
-query-qmp-schema
-----------------
-
-Return the QMP wire schema.  The returned value is a json-array of
-named schema entities.  Entities are commands, events and various
-types.  See docs/qapi-code-gen.txt for information on their structure
-and intended use.