Remove xcconfig from main project and custom projects

[BPerlakiH]

It turned out we can simplify the app configuration by relying only on .plist file values, therefore we can remove the xcconfig files.

[BPerlakiH]

Currently the xcconfig file was containing the final value for APP_STORE_ID, and it was used in custom apps for other values as well.
Each target (the Kiwix app, and each custom app) had its own Info.plist file and xcconfig.
It turned out that we can simplify this process with inlining the values required for both Kiwix app and custom apps into the info plist file, and we can remove all xcconfig files, as this way they won't be needed.
This simplifies the whole process.

[BPerlakiH]

In order to achieve this both the kiwix/apple and the kiwix/kiwix-apple-custom repositories need to be updated.

[BPerlakiH]

Implemented