Kill QueueSpan

As we move to writing large blocks, QueueSpan is only used for the log
file header, and was just calling CopyMessage.  Update the callers.

Change-Id: I50c79f653cda2c5bf9d401c52a59b5a1698285c1
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/events/logging/logfile_utils_test.cc b/aos/events/logging/logfile_utils_test.cc
index f453798..b3a9bbd 100644
--- a/aos/events/logging/logfile_utils_test.cc
+++ b/aos/events/logging/logfile_utils_test.cc
@@ -39,6 +39,10 @@
   void WriteSizedFlatbuffer(flatbuffers::DetachedBuffer &&buffer) {
     QueueSpan(absl::Span<const uint8_t>(buffer.data(), buffer.size()));
   }
+  void QueueSpan(absl::Span<const uint8_t> buffer) {
+    DataEncoder::SpanCopier coppier(buffer);
+    CopyMessage(&coppier, monotonic_clock::now());
+  }
 };
 
 // Creates a size prefixed flatbuffer from json.