doc: fix dcerpc.opnum documentation

Docs were claiming greater than, less than, etc. support even though this was never supported.

Fixes: 51be8f0238 ("doc/dcerpc: add proto keywords")

Ticket: #8330.

doc/userguide/rules/dcerpc-keywords.rst

@@ -43,18 +43,18 @@ interface in a DCERPC header.
 The format of the keyword::
 
   dcerpc.opnum:<u16>;
-  dcerpc.opnum:[>,<,!,=]<u16>;
   dcerpc.opnum:<u16>,<u16>,<u16>....;
   dcerpc.opnum:<u16>-<u16>;
 
 Examples::
 
   dcerpc.opnum:15;
-  dcerpc.opnum:>10;
   dcerpc.opnum:12,24,62,61;
   dcerpc.opnum:12,18-24,5;
   dcerpc.opnum:12-14,12,121,62-78;
 
+.. note:: earlier versions of the documentation incorrectly stated that greater than, less than, etc. notation was supported. This may be added later, see ticket `#8179 <https://redmine.openinfosecfoundation.org/issues/8179>`_).
+
 dcerpc.stub_data
 ----------------