orca-slicer: remove FLATPAK option

Currently, this breaks building, as this option requires wxGTK3 with
webkit2gtk-4.1 support. As there is no release yet with support for that
and backporting https://github.com/wxWidgets/wxWidgets/pull/23633 is
difficult, let's revert to the previous (vendored) build behavior.

Previously introduced in 0a92232f3f

Signed-off-by: Sefa Eyeoglu <contact@scrumplex.net>

pkgs/by-name/or/orca-slicer/package.nix

@@ -28,6 +28,8 @@ bambu-studio.overrideAttrs (
       )
     '';
 
+    cmakeFlags = lib.remove "-DFLATPAK=1" previousAttrs.cmakeFlags or [ ];
+
     # needed to prevent collisions between the LICENSE.txt files of
     # bambu-studio and orca-slicer.
     postInstall = ''