Remove already obsolete CREDENTIAL frame from SPDY code.

net/spdy/spdy_test_util_common.h

Index: net/spdy/spdy_test_util_common.h
diff --git a/net/spdy/spdy_test_util_common.h b/net/spdy/spdy_test_util_common.h
index b997c6acbf14bb5d842ec4f506a4806e81af4ab9..db6e65cf62c22398e38ea0d88772e97761fafc11 100644
--- a/net/spdy/spdy_test_util_common.h
+++ b/net/spdy/spdy_test_util_common.h
@@ -136,15 +136,12 @@ class StreamReleaserCallback : public TestCompletionCallbackBase {
   void OnComplete(SpdyStreamRequest* request, int result);
 };
 
-const size_t kSpdyCredentialSlotUnused = 0;
-
 // This struct holds information used to construct spdy control and data frames.
 struct SpdyHeaderInfo {
   SpdyFrameType kind;
   SpdyStreamId id;
   SpdyStreamId assoc_id;
   SpdyPriority priority;
-  size_t credential_slot;  // SPDY3 only
   SpdyControlFlags control_flags;
   bool compressed;
   SpdyRstStreamStatus status;