remoting: Cleanup class/struct fwd declarations

remoting/host/desktop_environment.h

Index: remoting/host/desktop_environment.h
diff --git a/remoting/host/desktop_environment.h b/remoting/host/desktop_environment.h
index 525dfbee98ff85a548934ee747288bb6c17df402..1e99bcfde90dc6dead3dbbbc8897deb05d27a021 100644
--- a/remoting/host/desktop_environment.h
+++ b/remoting/host/desktop_environment.h
@@ -14,10 +14,6 @@
 #include "base/memory/weak_ptr.h"
 #include "remoting/host/desktop_environment_options.h"
 
-namespace base {
-class SingleThreadTaskRunner;
-}  // namespace base
-
 namespace webrtc {
 class DesktopCapturer;
 class MouseCursorMonitor;
@@ -25,10 +21,6 @@ class MouseCursorMonitor;
 
 namespace remoting {
 
-namespace protocol {
-class ClientStub;
-}  // namespace protocol
-
 class AudioCapturer;
 class ClientSessionControl;
 class InputInjector;