Remove duplicate and outdated parts of database

[teutoburg]

• The top-level README in the database (not the root README!) did not contain any useful information, but some outdated TODO list and whatever.
• The three library-level README contained only information also found in the corresponding index.yml, where it was much better structured anyway.
• The two libraries "etc/pickles" and "etc/kinney" (aka "kc96") were duplicated subsets.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.61%. Comparing base (32caf38) to head (181e426).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #124   +/-   ##
=======================================
  Coverage   76.61%   76.61%           
=======================================
  Files           8        8           
  Lines         804      804           
=======================================
  Hits          616      616           
  Misses        188      188           

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