docs: taxhub_url parameter is no longer configurable from UI

[camillemonchicourt]

Also to remove in https://github.com/PnX-SI/gn_mobile_core/blob/develop/datasync/src/test/resources/fixtures/settings_sync.json ? And other files from this repository ?

I also think it would be good to merge develop into master in this repository.

[sgrimault]

docs/settings.adoc should be deleted as well (no longer used) as it describes requested settings for old "Sync" app. master branch will be updated from develop when an "official" release of "Occtax" app will be published.

[camillemonchicourt]

OK I let you change that as I dont want to do mistakes.