[css-display-3][editorial] Separate out the Privacy from Security section, now that that's a requirement.

Author: tabatkins

css-display-3/Overview.bs

@@ -2143,7 +2143,12 @@ Changes Prior to Candidate Recommendation Status</h3>
 			that are intended to accomplish this purpose.)
 	</ul>
 
-<h2 id="priv-sec" class="no-num">
-Privacy and Security Considerations</h2>
+<h2 id="priv" class="no-num">
+Privacy Considerations</h2>
 
-This specification introduces no new privacy or security considerations.
+This specification introduces no new privacy considerations.
+
+<h3 id="sec" class="no-num">
+Security Considerations</h2>
+
+This specification introduces no new security considerations.