[video_player] Remove package in example AndroidManifest.xml file (#10245)

discovered while investigating [#176575](flutter/flutter#176575)
opening the `example/android` folder in android studio , this warning appears `along others` :
```logs
> Task :app:processDebugMainManifest
package="io.flutter.plugins.videoplayerexample" found in source AndroidManifest.xml: video_player\video_player\example\android\app\src\main\AndroidManifest.xml.
Setting the namespace via the package attribute in the source AndroidManifest.xml is no longer supported, and the value is ignored.
Recommendation: remove package="io.flutter.plugins.videoplayerexample" from the source AndroidManifest.xml: video_player\video_player\example\android\app\src\main\AndroidManifest.xml.
```

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Author: AbdeMohlbi

packages/video_player/video_player/example/android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,4 @@
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-  package="io.flutter.plugins.videoplayerexample">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
   <application
     android:icon="@mipmap/ic_launcher"