libjack2: remove unused eigen dependency

The eigen dependency was added in 9d0441434d to support the iio plugin.
This plugin however was never included in our libjack.
Reason is, upstream requires both eigen and gtkIOStream for iio [1].

gtkIOstream [2] is mostly unmaintained upstream
and not even packaged in nixpkgs.
This means the eigen dependency is currently effectively unused.

[1] https://github.com/jackaudio/jack2/blob/43e1173e3060b2ebc9b6c54058464d5145afbf6e/wscript#L140-L149
[2] https://github.com/flatmax/gtkiostream

pkgs/misc/jackaudio/default.nix

@@ -9,7 +9,6 @@
   libsamplerate,
   libsndfile,
   readline,
-  eigen,
   celt,
   wafHook,
   # Darwin Dependencies
@@ -73,7 +72,6 @@ stdenv.mkDerivation (finalAttrs: {
       libsamplerate
       libsndfile
       readline
-      eigen
       celt
       optDbus
       optPythonDBus