fix(firefox): Fix simulcast on FF ESR

Make sure we don't have a=simulcast lines on the sendonly m-lines in the remote description

modules/RTC/TPCUtils.js

@@ -122,8 +122,16 @@ export class TPCUtils {
                 if (mline.type === 'video' && i !== idx) {
                     sdp.media[i].rids = undefined;
                     sdp.media[i].simulcast = undefined;
+
+                    // eslint-disable-next-line camelcase
+                    sdp.media[i].simulcast_03 = undefined;
                 }
             });
+
+            return new RTCSessionDescription({
+                type: desc.type,
+                sdp: transform.write(sdp)
+            });
         }
 
         // In order of highest to lowest spatial quality

modules/RTC/TraceablePeerConnection.js

@@ -1296,7 +1296,7 @@ TraceablePeerConnection.prototype._injectSsrcGroupForUnifiedSimulcast
         const sdp = transform.parse(desc.sdp);
         const video = sdp.media.find(mline => mline.type === 'video');
 
-        if (video.simulcast) {
+        if (video.simulcast || video.simulcast_03) {
             const ssrcs = [];
 
             video.ssrcs.forEach(ssrc => {