Remove obsolete FAQ information about Prioritized Background Activity

[MikeMcC399]

This PR resolves issue #2812 "Outdated instructions for Prioritized Background Activity".

For the FAQ articles:

• https://www.coronawarn.app/en/faq/results/#no_risk_update "[Google/Android]: My risk status hasn't been updated for over a day. An internet connection was available, what's wrong?"
• https://www.coronawarn.app/de/faq/results/#no_risk_update "[Google/Android]: Mein Risikostatus wurde seit über einem Tag nicht mehr aktualisiert. Internet war aber verfügbar, was läuft hier falsch?"

It removes text which only applied to CWA versions 1.5 and earlier, where it was possible to enable "Prioritized Background Activity" from within the app.

In the English version the paragraph advising to open the app daily is removed. This paragraph was not present in the German version. In the last months there have been no significant reports in GitHub describing this problem, so we can assume that the advice is no longer needed.

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Internal Tracking ID: EXPOSUREAPP-14431

[larswmh]

Thanks for providing a PR for this @MikeMcC399!