Settings fixes (hiding of old account warning)

[SystemKeeper]

This PR fixes 2 small issues:

• When the cache is cleared, we do not recalculate the size, resulting in the same size shown after clearing Done in https://github.com/nextcloud/talk-ios/pull/1851
• When the warning about a call from an old account is acknowledged, we don't reload the table view. Tapping again on the entry crashes the app.

Best to review commit by commit

[Ivansss]

/backport to stable20