net: remove UsingTCPFastOpen() method from StreamSocket class

net/socket/unix_domain_client_socket_posix.cc

Index: net/socket/unix_domain_client_socket_posix.cc
diff --git a/net/socket/unix_domain_client_socket_posix.cc b/net/socket/unix_domain_client_socket_posix.cc
index 9f7c3308e621adbdd31e834838398eb4b02c98f0..792cfac9bd299c63b530559561219728dd385293 100644
--- a/net/socket/unix_domain_client_socket_posix.cc
+++ b/net/socket/unix_domain_client_socket_posix.cc
@@ -131,10 +131,6 @@ bool UnixDomainClientSocket::WasEverUsed() const {
   return true;  // We don't care.
 }
 
-bool UnixDomainClientSocket::UsingTCPFastOpen() const {
-  return false;
-}
-
 bool UnixDomainClientSocket::WasNpnNegotiated() const {
   return false;
 }