There are no new releases of sqldeveloper v17/v18 and I don't think that
we should keep obviously unmaintained software that interacts with
database systems.
I removed `sqldeveloper_18` and `pkgs.sqldeveloper` now points to
version 19.4. Unfortunately I had to drop darwin support as JavaFX is
required for 19.4 which is part of the `oraclejdk` which isn't packaged
for darwin yet.
For further information please refer to the release notes:
https://www.oracle.com/technetwork/developer-tools/sql-developer/downloads/sqldev-relnotes-194-5908846.html
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