Issue #2332 - Update most tests to skip RTCSessionDescription construction

Backport of https://bugzilla.mozilla.org/show_bug.cgi?id=1263312 part 6

dom/media/tests/mochitest/test_peerConnection_remoteRollback.html

@@ -20,10 +20,8 @@
       function PC_REMOTE_ROLLBACK(test) {
         // We still haven't negotiated the tracks
         test.pcRemote.expectNegotiationNeeded();
-        return test.setRemoteDescription(
-          test.pcRemote,
-          new RTCSessionDescription({ type: "rollback" }),
-          STABLE)
+        return test.setRemoteDescription(test.pcRemote, { type: "rollback" },
+                                         STABLE)
           .then(() => test.pcRemote.rollbackRemoteTracksIfNotNegotiated());
       },