Deprecate --gfe2_reloadable_flag_quic_ack_cid_frames.

PiperOrigin-RevId: 397761749
diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index 4e48912..05b5d88 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -2015,10 +2015,7 @@
   if (perspective_ == Perspective::IS_SERVER) {
     OnClientConnectionIdAvailable();
   }
-  if (ack_cid_frames_) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_ack_cid_frames, 1, 2);
-    MaybeUpdateAckTimeout();
-  }
+  MaybeUpdateAckTimeout();
   return true;
 }
 
@@ -2078,10 +2075,7 @@
   }
   // Count successfully received RETIRE_CONNECTION_ID frames.
   QUIC_RELOADABLE_FLAG_COUNT_N(quic_connection_migration_use_new_cid_v2, 5, 6);
-  if (ack_cid_frames_) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_ack_cid_frames, 2, 2);
-    MaybeUpdateAckTimeout();
-  }
+  MaybeUpdateAckTimeout();
   return true;
 }
 
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index 77f5266..f05d2e0 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -2287,8 +2287,6 @@
   const bool add_missing_update_ack_timeout_ =
       GetQuicReloadableFlag(quic_add_missing_update_ack_timeout);
 
-  const bool ack_cid_frames_ = GetQuicReloadableFlag(quic_ack_cid_frames);
-
   const bool use_active_cid_for_session_lookup_ =
       GetQuicReloadableFlag(quic_use_active_cid_for_session_lookup);
 };
diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index a3b9f90..64a8402 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc
@@ -12185,13 +12185,9 @@
   new_writer.SetWritable();
   // Write event on the default socket shouldn't make any difference.
   connection_.OnCanWrite();
-  if (GetQuicReloadableFlag(quic_ack_cid_frames)) {
-    // A NEW_CONNECTION_ID frame is received in PathProbeTestInit and OnCanWrite
-    // will write a acking packet.
-    EXPECT_EQ(1u, writer_->packets_write_attempts());
-  } else {
-    EXPECT_EQ(0u, writer_->packets_write_attempts());
-  }
+  // A NEW_CONNECTION_ID frame is received in PathProbeTestInit and OnCanWrite
+  // will write a acking packet.
+  EXPECT_EQ(1u, writer_->packets_write_attempts());
   EXPECT_EQ(1u, new_writer.packets_write_attempts());
 }
 
@@ -15349,7 +15345,6 @@
   connection_.SetFromConfig(config);
   if (!version().HasIetfQuicFrames() ||
       !connection_.connection_migration_use_new_cid() ||
-      !GetQuicReloadableFlag(quic_ack_cid_frames) ||
       !GetQuicReloadableFlag(quic_add_missing_update_ack_timeout)) {
     return;
   }
diff --git a/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index 9abf6d9..c9c9bdf 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -105,8 +105,6 @@
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_suppress_write_mid_packet_processing, true)
 // If true, time_wait_list can support multiple connection IDs.
 QUIC_FLAG(FLAGS_quic_restart_flag_quic_time_wait_list_support_multiple_cid_v2, true)
-// If true, update ACK timeout for NEW_CONNECTION_ID and RETIRE_CONNECTION_ID frames.
-QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_ack_cid_frames, true)
 // If true, use BBRv2 as the default congestion controller. Takes precedence over --quic_default_to_bbr.
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_default_to_bbr_v2, false)
 // If true, use new connection ID in connection migration.