Remove manifest package name

As reported by gradle:

> Setting the namespace via a source AndroidManifest.xml's package
> attribute is deprecated.
>
> Please instead set the namespace (or testNamespace) in the module's
> build.gradle file, as described here:
> https://developer.android.com/studio/build/configure-app-module#set-namespace

server/src/main/AndroidManifest.xml

@@ -1,2 +1,2 @@
 <!-- not a real Android application, it is run by app_process manually -->
-<manifest package="com.genymobile.scrcpy"/>
+<manifest />