Delete unused function SetSessionError.

session/media/channel.cc

Index: session/media/channel.cc
diff --git a/session/media/channel.cc b/session/media/channel.cc
index 8de8d379962e2aec5936ce9a2e04d11860c629e1..5eec47cc4eae4a75ddc4803b607ea868b0600112 100644
--- a/session/media/channel.cc
+++ b/session/media/channel.cc
@@ -60,11 +60,6 @@ static const char kDtlsSrtpExporterLabel[] = "EXTRACTOR-dtls_srtp";
 
 static const int kAgcMinus10db = -10;
 
-static void SetSessionError(BaseSession* session, BaseSession::Error error,
-                            const std::string& error_desc) {
-  session->SetError(error, error_desc);
-}
-
 static void SafeSetError(const std::string& message, std::string* error_desc) {
   if (error_desc) {
     *error_desc = message;