Remove references to APKPure, because it distributes some malware

[Olf0]

Partially fixes issue #401, i.e. its whole point 2, but not point 1; for detailed reasoning, see there.

[jovirkku]

This sentence (although modified) on line 44 must remain - it is becoming more valid on 4.6.0:

Note that "Settings > System > Untrusted software" must be enabled to install Android apps, too.

UPDATE:
Or perhaps not as it is well stated at the beginning of Help_Articles/Android_App_Support/README.md

[Olf0]

UPDATE: Or perhaps not as it is well stated at the beginning of Help_Articles/Android_App_Support/README.md

Exactly!
There was some duplicated information in these articles and I tried to deduplicate it, because duplicated information is hard to maintain in parallel and hence tends to become out-of-sync, which confuses users.

You already pointed to the central article for AAS: /Support/Help_Articles/Android_App_Support/README.md
Details with regard to AAS should be aggregated there. Furthermore this article directly links to it, see https://github.com/sailfishos/docs.sailfishos.org/pull/404/files#diff-cb55aa306d42f320ed6e0b909ae08330e7927817f84062aadd128a79700b391bR44. Consequently re-duplicating this information is counterproductive.

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Side note / question:

This sentence (although modified) on line 44 must remain - it is becoming more valid on 4.6.0:

Note that "Settings > System > Untrusted software" must be enabled to install Android apps, too.

I wonder what "more valid" is supposed to mean:

1. Does the installation of an APK from the file system via the Settings app's file browser respectively the native apps File Browser and FileCase (e.g. for the initial installation of a downloaded APK of an Android app store client by GUI means) require "Allow untrusted software" to be switched on, starting with SailfishOS 4.6.0?
2. Or does the installation of an APK by the help of an Android app store client app require "Allow untrusted software" to be switched on, starting with SailfishOS 4.6.0? (This would be bad and disruptive!)

IIRC "Allow untrusted software" only affected SailfishOS-native apps on SailfishOS < 4.6.0, correct?