sqldeveloper: {17.4.1.054.0712,18.2.0.183.1748} -> 19.4.0.354.1759

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