Remove |frame_len| argument from OnHeadersFrameEnd().

At cr/231494986 I end up using the |frame_length| argument of
OnHeadersFrameStart(), leaving the argument of OnHeadersFrameEnd()
unused.

This partially reverts cr/233149295, which turns out was a bad guess.
Sorry.

gfe-relnote: n/a.  Remove unused argument, no functional change.
PiperOrigin-RevId: 243272208
Change-Id: If163cf3d9c6532cefaa5c9d9874c522607237f72
diff --git a/quic/core/http/quic_spdy_stream.h b/quic/core/http/quic_spdy_stream.h
index 6d2f9b1..c1bb95a 100644
--- a/quic/core/http/quic_spdy_stream.h
+++ b/quic/core/http/quic_spdy_stream.h
@@ -207,7 +207,7 @@
   void OnDataFrameEnd();
   void OnHeadersFrameStart(Http3FrameLengths frame_length);
   void OnHeadersFramePayload(QuicStringPiece payload);
-  void OnHeadersFrameEnd(QuicByteCount frame_len);
+  void OnHeadersFrameEnd();
 
   // Called when the received headers are too large. By default this will
   // reset the stream.