Remove QuicUtils::ListTags and use ToDebugString() instead.

net/quic/core/quic_utils.cc

Index: net/quic/core/quic_utils.cc
diff --git a/net/quic/core/quic_utils.cc b/net/quic/core/quic_utils.cc
index f02adfc2094d071f2cfb9c569e184dae522a7192..25cb2d4436a690f3778c267861aa59df97f9f7aa 100644
--- a/net/quic/core/quic_utils.cc
+++ b/net/quic/core/quic_utils.cc
@@ -381,14 +381,6 @@ QuicTagVector QuicUtils::ParseQuicConnectionOptions(
   return options;
 }
 
-string QuicUtils::ListTags(QuicTagValueMap tag_map) {
-  string result;
-  for (auto entry : tag_map) {
-    result.append(TagToString(entry.first) + " ");
-  }
-  return result;
-}
-
 string QuicUtils::PeerAddressChangeTypeToString(PeerAddressChangeType type) {
   switch (type) {
     RETURN_STRING_LITERAL(NO_CHANGE);