Make the RtpHeaderParserImpl available to tests and tools only.

There are a few reasons for making this test only:
* The code is only used by tests and utilities.
* The pure interface has only a single implementation so an interface isn't really needed.
  (a followup change could remove it altogether)
* The implementation always incorporates locking regardless of how the class gets used.
  See e.g. previous use in the Packet class.
* The implementation is a layer on top of RtpUtility::RtpHeaderParser which is
  sufficient for most production cases.

Change-Id: Ide6d50567cf8ae5127a2eb04cceeb10cf317ec36
Bug: none
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150658
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29010}
diff --git a/test/scenario/call_client.cc b/test/scenario/call_client.cc
index 31435bb..1654afc 100644
--- a/test/scenario/call_client.cc
+++ b/test/scenario/call_client.cc
@@ -203,7 +203,7 @@
       clock_(time_controller->GetClock()),
       log_writer_factory_(std::move(log_writer_factory)),
       network_controller_factory_(log_writer_factory_.get(), config.transport),
-      header_parser_(RtpHeaderParser::Create()),
+      header_parser_(RtpHeaderParser::CreateForTest()),
       task_queue_(time_controller->GetTaskQueueFactory()->CreateTaskQueue(
           "CallClient",
           TaskQueueFactory::Priority::NORMAL)) {