Remove AudioDeviceObserver and make ADM not inherit from the Module interface.

modules/include/module.h

Index: modules/include/module.h
diff --git a/modules/include/module.h b/modules/include/module.h
index becffb9ad3878105791ea785a07ac15c77406df0..fc2a1b5fc96eb2913bb2e37bc1f0257ffc5593ef 100644
--- a/modules/include/module.h
+++ b/modules/include/module.h
@@ -58,24 +58,6 @@ class Module {
  protected:
   virtual ~Module() {}
 };
-
-// Reference counted version of the Module interface.
-class RefCountedModule : public Module {
- public:
-  // Increase the reference count by one.
-  // Returns the incremented reference count.
-  virtual int32_t AddRef() const = 0;
-
-  // Decrease the reference count by one.
-  // Returns the decreased reference count.
-  // Returns 0 if the last reference was just released.
-  // When the reference count reaches 0 the object will self-destruct.
-  virtual int32_t Release() const = 0;
-
- protected:
-  ~RefCountedModule() override = default;
-};
-
 }  // namespace webrtc
 
 #endif  // MODULES_INCLUDE_MODULE_H_