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
(cherry picked from commit 2de89ca2ce)

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