Using mock transport controller in audio unit tests.

Using a mock of rtp transport controller send in audio send stream unit
tests. This reduces the dependencies and makes the tests more focused
on testing the functionality of audio send stream itself.

Bug: webrtc:8415
Change-Id: Ia8d9cf47d93decc74b10ca75a6771f39df658dc2
Reviewed-on: https://webrtc-review.googlesource.com/56600
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22161}
diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index 59302ea..618ec84 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -125,9 +125,9 @@
       ":audio_end_to_end_test",
       "../api:mock_audio_mixer",
       "../call:mock_call_interfaces",
+      "../call:mock_rtp_interfaces",
       "../call:rtp_interfaces",
       "../call:rtp_receiver",
-      "../call:rtp_sender",
       "../common_audio",
       "../logging:mocks",
       "../modules:module_api",