Remove unused server end points and don't mask errors at opening db maps

[manuelma]

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes in Toolbox repo have been updated
• [x] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [x] Unit tests pass

[codecov-commenter]

Codecov Report

Base: 74.40% // Head: 74.46% // Increases project coverage by +0.05% :tada:

Coverage data is based on head (4068d6d) compared to base (353fd33). Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #202 +/- ## ========================================== + Coverage 74.40% 74.46% +0.05% ========================================== Files 71 71 Lines 11711 11697 -14 Branches 2270 2270 ========================================== - Hits 8714 8710 -4 + Misses 2550 2540 -10 Partials 447 447 ``` | [Impacted Files](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project) | Coverage Δ | | |---|---|---| | [spinedb\_api/spine\_db\_client.py](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/202/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project#diff-c3BpbmVkYl9hcGkvc3BpbmVfZGJfY2xpZW50LnB5) | `48.93% <ø> (-0.09%)` | :arrow_down: | | [spinedb\_api/spine\_db\_server.py](https://codecov.io/gh/Spine-project/Spine-Database-API/pull/202/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project#diff-c3BpbmVkYl9hcGkvc3BpbmVfZGJfc2VydmVyLnB5) | `33.05% <0.00%> (+0.35%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project)

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