2269 remove find monkeys in db

[cakekoa]

What does this PR do?

Fixes part of #2269.

Refactors is_all_monkeys_dead, which freed up find_monkeys_in_db to be removed. Took the opportunity to refactor test_os_compat and remove get_all_monkeys_from_db as well.

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Have you successfully tested your changes locally? Elaborate:

  Tested by {Running the Monkey locally with relevant config/running Island/...}

• If applicable, add screenshots or log transcripts of the feature working

[codecov]

Codecov Report

Base: 61.17% // Head: 61.15% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (bbbb1ac) compared to base (a691a16).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2391      +/-   ##
===========================================
- Coverage    61.17%   61.15%   -0.02%     
===========================================
  Files          553      551       -2     
  Lines        14432    14404      -28     
===========================================
- Hits          8829     8809      -20     
+ Misses        5603     5595       -8     

Impacted Files	Coverage Δ
monkey/monkey_island/cc/app.py	80.28% <ø> (-0.55%)	⬇️

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