Revert "Add ability to set ssrcs of RtpSender at construction time"

This reverts commit e9d6e658c307fc0241d622756703d5c0d5388d80.

Reason for revert: breaks downstream project

Original change's description:
> Add ability to set ssrcs of RtpSender at construction time
> 
> Bug: webrtc:10774
> Change-Id: I7147a75ccbcd1093dcd2e08047da8900843fdd8d
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144037
> Commit-Queue: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Åsa Persson <asapersson@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#28447}

TBR=asapersson@webrtc.org,sprang@webrtc.org

Change-Id: I8b0cba0836e7d86ae1718055196c2c89860b97ff
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10774
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144368
Reviewed-by: Amit Hilbuch <amithi@webrtc.org>
Commit-Queue: Amit Hilbuch <amithi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28453}
diff --git a/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 21b85a1..f8a0d70 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -40,7 +40,6 @@
 }  // namespace
 
 RtpRtcp::Configuration::Configuration() = default;
-RtpRtcp::Configuration::Configuration(Configuration&& rhs) = default;
 
 std::unique_ptr<RtpRtcp> RtpRtcp::Create(const Configuration& configuration) {
   RTC_DCHECK(configuration.clock);
@@ -95,8 +94,27 @@
       ack_observer_(configuration.ack_observer),
       rtt_stats_(configuration.rtt_stats),
       rtt_ms_(0) {
+  FieldTrialBasedConfig default_trials;
   if (!configuration.receiver_only) {
-    rtp_sender_.reset(new RTPSender(configuration));
+    rtp_sender_.reset(new RTPSender(
+        configuration.audio, configuration.clock,
+        configuration.outgoing_transport, configuration.paced_sender,
+        configuration.flexfec_sender
+            ? absl::make_optional(configuration.flexfec_sender->ssrc())
+            : absl::nullopt,
+        configuration.transport_sequence_number_allocator,
+        configuration.transport_feedback_callback,
+        configuration.send_bitrate_observer,
+        configuration.send_side_delay_observer, configuration.event_log,
+        configuration.send_packet_observer,
+        configuration.retransmission_rate_limiter,
+        configuration.overhead_observer,
+        configuration.populate_network2_timestamp,
+        configuration.frame_encryptor, configuration.require_frame_encryption,
+        configuration.extmap_allow_mixed,
+        configuration.field_trials ? *configuration.field_trials
+                                   : default_trials));
+
     // Make sure rtcp sender use same timestamp offset as rtp sender.
     rtcp_sender_.SetTimestampOffset(rtp_sender_->TimestampOffset());
   }