Fix editorial error

There is no third snippet, the sentence was left over when removing the nested 

```
<section>
  <h1>
  <section>
    <h1>
```

pattern

sections/semantics-sections.include

@@ -864,8 +864,7 @@
     in the face of heavy editing; which is best is purely an issue of preferred authoring style.
 
     The two styles can be combined, for compatibility with legacy tools while still future-proofing
-    for when that compatibility is no longer needed. This third snippet again has the same outline
-    as the previous two:
+    for when that compatibility is no longer needed.
 
   </div>