Remove `eigenbedarf_gedeckt` from Kindergeldübertrag

[MImmesberger]

Closes #758

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.86%. Comparing base (3816876) to head (c8abdaf). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #786 +/- ## ========================================== + Coverage 89.79% 89.86% +0.06% ========================================== Files 53 53 Lines 3802 3807 +5 ========================================== + Hits 3414 3421 +7 + Misses 388 386 -2 ```

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[MImmesberger]

The only occurrence of eigenbedarf_gedeckt now is in the bg_id creation. I left it there intentionally because then we have a way to manually set the BGs until we get #763 right. If we replace it with the correct earnings check, we cannot compute scenarios where children + parents are in the same BG even when children have covered their needs for the time being (relevant for KiZ I think).

[hmgaudecker]

Fine. Then maybe add a to-do next to the input variable and in the bg_id creation, both linking #763. Just so that this is very visible!