Deprecate gfe2_reloadable_flag_quic_bbr_slower_startup4

gfe-relnote: n/a (Flag deprecation)
PiperOrigin-RevId: 287551870
Change-Id: I0b5a0ed40e93130a5b2f310291c3c35d2cefaf3e

quic/core/congestion_control/bbr_sender.cc

diff --git a/quic/core/congestion_control/bbr_sender.cc b/quic/core/congestion_control/bbr_sender.cc
index 4a583bb..b750e0a 100644
--- a/quic/core/congestion_control/bbr_sender.cc
+++ b/quic/core/congestion_control/bbr_sender.cc
@@ -319,9 +319,7 @@
   if (config.HasClientRequestedIndependentOption(kBBQ3, perspective)) {
     enable_ack_aggregation_during_startup_ = true;
   }
-  if (GetQuicReloadableFlag(quic_bbr_slower_startup4) &&
-      config.HasClientRequestedIndependentOption(kBBQ5, perspective)) {
-    QUIC_RELOADABLE_FLAG_COUNT(quic_bbr_slower_startup4);
+  if (config.HasClientRequestedIndependentOption(kBBQ5, perspective)) {
     expire_ack_aggregation_in_startup_ = true;
   }
   if (config.HasClientRequestedIndependentOption(kMIN1, perspective)) {