Replace left-over ASSERTs in httpcommon.h and webrtcsession.cc.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2630553003
Cr-Commit-Position: refs/heads/master@{#16055}
diff --git a/webrtc/api/webrtcsession.cc b/webrtc/api/webrtcsession.cc
index 30a0a7c..a0c72c8 100644
--- a/webrtc/api/webrtcsession.cc
+++ b/webrtc/api/webrtcsession.cc
@@ -2374,7 +2374,7 @@
 }
 
 void WebRtcSession::DestroyRtcpTransport_n(const std::string& transport_name) {
-  ASSERT(network_thread()->IsCurrent());
+  RTC_DCHECK(network_thread()->IsCurrent());
   transport_controller_->DestroyTransportChannel_n(
       transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTCP);
 }