Deprecate quic_allow_very_long_connection_ids

gfe-relnote: deprecate gfe2_restart_flag_quic_allow_very_long_connection_ids
PiperOrigin-RevId: 293391205
Change-Id: I075bf308aa3a7b668ccaaa67efdeecabd51df714
diff --git a/quic/core/quic_utils.cc b/quic/core/quic_utils.cc
index f5eecd7..8057a7d 100644
--- a/quic/core/quic_utils.cc
+++ b/quic/core/quic_utils.cc
@@ -548,13 +548,10 @@
     return false;
   }
 
-  if (GetQuicRestartFlag(quic_allow_very_long_connection_ids)) {
-    QUIC_RESTART_FLAG_COUNT_N(quic_allow_very_long_connection_ids, 5, 5);
-    if (transport_version == QUIC_VERSION_UNSUPPORTED ||
-        transport_version == QUIC_VERSION_RESERVED_FOR_NEGOTIATION) {
-      // Unknown versions could allow connection ID lengths up to 255.
-      return true;
-    }
+  if (transport_version == QUIC_VERSION_UNSUPPORTED ||
+      transport_version == QUIC_VERSION_RESERVED_FOR_NEGOTIATION) {
+    // Unknown versions could allow connection ID lengths up to 255.
+    return true;
   }
 
   const uint8_t connection_id_length8 =