Disable H4 title numbering

Signed-off-by: Roger Sheen <roger@infotexture.net>

Author: infotexture

samples/themes/dita-ot-docs-theme.yaml

@@ -149,6 +149,7 @@ style:
     font-size: 12pt
     font-style: italic
     space-before: 12pt
+    title-numbering: false
   li:
     label:
       color: $brand-color-secondary