Remove incorrect uses of GetHeadersStreamId().

Many places call GetHeadersStreamId() only to use the first stream id. So I
reaplced them with GetFirstBirectionalStreamId().

gfe-relnote: v99 and test change only, not protected.
PiperOrigin-RevId: 261412202
Change-Id: I54f3b5b5a100d8b8d31a0de5ecb324b474c6a430
diff --git a/quic/core/quic_utils.cc b/quic/core/quic_utils.cc
index 58996f6..1e2c5fc 100644
--- a/quic/core/quic_utils.cc
+++ b/quic/core/quic_utils.cc
@@ -401,7 +401,7 @@
 
 // static
 QuicStreamId QuicUtils::GetHeadersStreamId(QuicTransportVersion version) {
-  // TODO(b/138653948): Add DCHECK(!VersionUsesQpack(version));
+  DCHECK(!VersionUsesQpack(version));
   return GetFirstBidirectionalStreamId(version, Perspective::IS_CLIENT);
 }