Deprecate usage of `app1` in preferences

[david-allison]

:app should be http://schemas.android.com/apk/res-auto

Our use of http://arbitrary.app.namespace/com.ichi2.anki should be actually deprecated.

Originally posted by @BrayanDSO in #20001 (comment)

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Anki-Android/AnkiDroid/src/main/res/xml/preferences_dev_options.xml

Lines 21 to 23 in 7fbdfbf

	<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
	xmlns:app="http://arbitrary.app.namespace/com.ichi2.anki"
	xmlns:app1="http://schemas.android.com/apk/res-auto"

[pankaj0695]

Can I work on this?

[david-allison]

Sure!