Removes templating from CompositeMediaEngine.

Usage of templates makes it harder for tooling to help the user. This
can be experienced when trying to investigate compile failures and using
editor tools to browse the code.

This CL replaces usage of templates with injection of unique pointers to
interfaces that implements the behavior that previously was assumed by
the templated implementation.

Bug: webrtc:9883
Change-Id: Ica17af9646f68a9b063988f9e85d6acc8ca37c10
Reviewed-on: https://webrtc-review.googlesource.com/c/106703
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25668}
diff --git a/media/base/fakemediaengine.h b/media/base/fakemediaengine.h
index 4821ad4..d7b44c5 100644
--- a/media/base/fakemediaengine.h
+++ b/media/base/fakemediaengine.h
@@ -554,8 +554,7 @@
   friend class FakeMediaEngine;
 };
 
-class FakeMediaEngine
-    : public CompositeMediaEngine<FakeVoiceEngine, FakeVideoEngine> {
+class FakeMediaEngine : public CompositeMediaEngine {
  public:
   FakeMediaEngine();