Deprecate --gfe2_reloadable_flag_quic_save_user_agent_in_quic_session.

PiperOrigin-RevId: 325802181
Change-Id: Ib08bfff5478c70a57d5062ed02f4c39ddfed513e
diff --git a/quic/core/http/quic_spdy_stream.cc b/quic/core/http/quic_spdy_stream.cc
index 4c979c1..7dfe1fe 100644
--- a/quic/core/http/quic_spdy_stream.cc
+++ b/quic/core/http/quic_spdy_stream.cc
@@ -529,19 +529,15 @@
 void QuicSpdyStream::OnStreamHeaderList(bool fin,
                                         size_t frame_len,
                                         const QuicHeaderList& header_list) {
-  if (GetQuicReloadableFlag(quic_save_user_agent_in_quic_session)) {
-    if (!spdy_session()->user_agent_id().has_value()) {
-      QUIC_RELOADABLE_FLAG_COUNT_N(quic_save_user_agent_in_quic_session, 3, 3);
-      std::string uaid;
-      for (const auto& kv : header_list) {
-        if (quiche::QuicheTextUtils::ToLower(kv.first) ==
-            kUserAgentHeaderName) {
-          uaid = kv.second;
-          break;
-        }
+  if (!spdy_session()->user_agent_id().has_value()) {
+    std::string uaid;
+    for (const auto& kv : header_list) {
+      if (quiche::QuicheTextUtils::ToLower(kv.first) == kUserAgentHeaderName) {
+        uaid = kv.second;
+        break;
       }
-      spdy_session()->SetUserAgentId(std::move(uaid));
     }
+    spdy_session()->SetUserAgentId(std::move(uaid));
   }
 
   // TODO(b/134706391): remove |fin| argument.