deja-dup: remove unneeded rpath wrapping

[jtojnar]

Motivation for this change

Similarly to 9e37df1 and #31218, I cleaned up deja-dup. Unfortunately, deja-dup requires a custom library in $ORIGIN/../lib/deja-dup and meson for some reason adds $ORIGIN/../libdeja to the rpath (see #31222).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[jtojnar]

This can be further simplified when #31436 is merged.