plantuml-server: fixed unstable deps

[nazarewk]

after merging #163431 plantuml-server-*-deps derivation turned out unstable, this commit switches to fetching plantuml.war directly from releases

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/):
  1. nix build '.#plantuml-server' '.#jdk' '.#jetty' into
  2. "${PWD}/result-1/bin/java" -jar "${PWD}/result-2/start.jar" --module=deploy,http,jsp jetty.home="${PWD}/result-2" jetty.base="${PWD}/result" jetty.http.host=127.0.0.1 jetty.http.port=7890
  3. visit http://127.0.0.1:7890/plantuml in a browser and tried to render something
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.