Deprecate gfe2_reloadable_flag_quic_bbr_slower_startup3.

gfe-relnote: n/a (Flag deprecation)
PiperOrigin-RevId: 253789248
Change-Id: I60fbed57d294d397878df317a4ea0b0507d2be8d
diff --git a/quic/core/congestion_control/bbr_sender.cc b/quic/core/congestion_control/bbr_sender.cc
index c455751..858e57d 100644
--- a/quic/core/congestion_control/bbr_sender.cc
+++ b/quic/core/congestion_control/bbr_sender.cc
@@ -310,21 +310,15 @@
     QUIC_RELOADABLE_FLAG_COUNT(quic_bbr_flexible_app_limited);
     flexible_app_limited_ = true;
   }
-  if (GetQuicReloadableFlag(quic_bbr_slower_startup3) &&
-      config.HasClientRequestedIndependentOption(kBBQ1, perspective)) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr_slower_startup3, 1, 4);
+  if (config.HasClientRequestedIndependentOption(kBBQ1, perspective)) {
     set_high_gain(kDerivedHighGain);
     set_high_cwnd_gain(kDerivedHighGain);
     set_drain_gain(1.f / kDerivedHighGain);
   }
-  if (GetQuicReloadableFlag(quic_bbr_slower_startup3) &&
-      config.HasClientRequestedIndependentOption(kBBQ2, perspective)) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr_slower_startup3, 2, 4);
+  if (config.HasClientRequestedIndependentOption(kBBQ2, perspective)) {
     set_high_cwnd_gain(kDerivedHighCWNDGain);
   }
-  if (GetQuicReloadableFlag(quic_bbr_slower_startup3) &&
-      config.HasClientRequestedIndependentOption(kBBQ3, perspective)) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_bbr_slower_startup3, 3, 4);
+  if (config.HasClientRequestedIndependentOption(kBBQ3, perspective)) {
     enable_ack_aggregation_during_startup_ = true;
   }
   if (GetQuicReloadableFlag(quic_bbr_slower_startup4) &&