Deprecate quic_parse_prox_source_connection_id

gfe-relnote: deprecate gfe2_reloadable_flag_quic_parse_prox_source_connection_id
PiperOrigin-RevId: 278406183
Change-Id: I474d0fe018c74ce9982e87f248e40052401ca336

quic/core/quic_framer.cc

diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index 756788f..761645e 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -6255,9 +6255,7 @@
       return false;
     }
     if (!reader->ReadLengthPrefixedConnectionId(source_connection_id)) {
-      if (GetQuicReloadableFlag(quic_parse_prox_source_connection_id) &&
-          version_label == kProxVersionLabel) {
-        QUIC_RELOADABLE_FLAG_COUNT(quic_parse_prox_source_connection_id);
+      if (version_label == kProxVersionLabel) {
         // The "PROX" version does not follow the length-prefixed invariants,
         // and can therefore attempt to read a payload byte and interpret it
         // as the source connection ID length, which could fail to parse.

quic/core/quic_framer_test.cc

diff --git a/quic/core/quic_framer_test.cc b/quic/core/quic_framer_test.cc
index 38d222b..3b0e879 100644
--- a/quic/core/quic_framer_test.cc
+++ b/quic/core/quic_framer_test.cc
@@ -1294,7 +1294,6 @@
   if (!framer_.version().HasLengthPrefixedConnectionIds()) {
     return;
   }
-  SetQuicReloadableFlag(quic_parse_prox_source_connection_id, true);
   // clang-format off
   unsigned char packet[] = {
     // public flags (long header with packet type HANDSHAKE and