video_mixer: remove useless switchInput

This switch input can be long and is not useful

Gitlab: #272
Change-Id: I53363f820e15431af55dcf0610451efc84a41d02

src/media/video/video_mixer.cpp

@@ -68,10 +68,8 @@ VideoMixer::VideoMixer(const std::string& id)
 {
     // Local video camera is the main participant
     videoLocal_ = getVideoCamera();
-    if (videoLocal_) {
-        DRing::switchToCamera();
+    if (videoLocal_)
         videoLocal_->attach(this);
-    }
     loop_.start();
 }