Remove one use of sigslot from webrtc_session_description_factory

This instance turned out to only be used for a single constant, known at
creation time callback function, so a function was more appropriate.

Bug: none
Change-Id: If131f75ed82607af50c4d85f1e80a693170ff687
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/192362
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32569}
diff --git a/pc/sdp_offer_answer.cc b/pc/sdp_offer_answer.cc
index 7902a35..fd697ce 100644
--- a/pc/sdp_offer_answer.cc
+++ b/pc/sdp_offer_answer.cc
@@ -994,9 +994,10 @@
       std::make_unique<WebRtcSessionDescriptionFactory>(
           signaling_thread(), channel_manager(), this, pc_->session_id(),
           pc_->dtls_enabled(), std::move(dependencies.cert_generator),
-          certificate, &ssrc_generator_);
-  webrtc_session_desc_factory_->SignalCertificateReady.connect(
-      this, &SdpOfferAnswerHandler::OnCertificateReady);
+          certificate, &ssrc_generator_,
+          [this](const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
+            transport_controller()->SetLocalCertificate(certificate);
+          });
 
   if (pc_->options()->disable_encryption) {
     webrtc_session_desc_factory_->SetSdesPolicy(cricket::SEC_DISABLED);
@@ -1061,11 +1062,6 @@
 
 // ===================================================================
 
-void SdpOfferAnswerHandler::OnCertificateReady(
-    const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
-  transport_controller()->SetLocalCertificate(certificate);
-}
-
 void SdpOfferAnswerHandler::PrepareForShutdown() {
   RTC_DCHECK_RUN_ON(signaling_thread());
   weak_ptr_factory_.InvalidateWeakPtrs();