Work around new requirements from respec for updated recs

instead of using a configuration key, respec now search for markup to determine whether a spec contains corrections or additions; but since the markup is added as post-processing in this spec, the detection fails. Instead, adding hidden markup to trigger the right effect.

That markup will have to have the classes proposed-addition / proposed-correction if/when we reach that status

webrtc.html

@@ -42,7 +42,7 @@
       </p>
     </section>
     <section id="sotd" class="updateable-rec">
-      <p>This document includes <a href="#changes">Candidate Amendments</a> to the current <a href="https://www.w3.org/TR/2021/REC-webrtc-20210126/">W3C Recommendation dated January 26, 2021</a>.</p>
+      <p><span hidden class="correction addition"></span>This document includes <a href="#changes" >Candidate Amendments</a> to the current <a href="https://www.w3.org/TR/2021/REC-webrtc-20210126/">W3C Recommendation dated January 26, 2021</a>.</p>
       <p>
         Its <a href=
         "https://github.com/web-platform-tests/wpt/tree/master/webrtc">associated

webrtc.js

@@ -77,7 +77,6 @@ var respecConfig = {
 
   testSuiteURI: "https://github.com/web-platform-tests/wpt/tree/master/webrtc/",
   implementationReportURI: "https://w3c.github.io/webrtc-interop-reports/webrtc-pc-report.html",
-  revisionTypes: ["addition", "correction"],
   lint: {
     "wpt-tests-exist": true
   },