Remove unnecessary Activity method overrides in session demo app

The PlayerView methods are documented to only be needed for sphrerical
playbacks, which we are not using in the session demo app.

PiperOrigin-RevId: 525986709

demos/session/src/main/java/androidx/media3/demo/session/PlayerActivity.kt

@@ -88,16 +88,6 @@ class PlayerActivity : AppCompatActivity() {
     initializeController()
   }
 
-  override fun onResume() {
-    super.onResume()
-    playerView.onResume()
-  }
-
-  override fun onPause() {
-    super.onPause()
-    playerView.onPause()
-  }
-
   override fun onStop() {
     super.onStop()
     playerView.player = null