zoom-us: reintroduce unset QT_PLUGIN_PATH

This was introduced long ago here

https://github.com/NixOS/nixpkgs/pull/116355
https://github.com/NixOS/nixpkgs/commit/b747aa0f9fd6363975e90a82210275a12bfbb696

to fix a display problem (participants dialog box).

With one of the more recent updates,
the workaround was no longer needed to fix
the original problem, so it was removed here

https://github.com/NixOS/nixpkgs/pull/425420
https://github.com/NixOS/nixpkgs/commit/c3a86691ba8aebe32cedbfc72e3b738f2bf93a1f

However, it turned out the workaround is still needed
to keep zoom happy in other environments, cf.

https://github.com/NixOS/nixpkgs/issues/428434
https://github.com/NixOS/nixpkgs/issues/429341

pkgs/by-name/zo/zoom-us/package.nix

@@ -243,6 +243,7 @@ else
     inherit (unpacked) pname version;
 
     targetPkgs = pkgs: (linuxGetDependencies pkgs) ++ [ unpacked ];
+    extraPreBwrapCmds = "unset QT_PLUGIN_PATH";
     extraBwrapArgs = [ "--ro-bind ${unpacked}/opt /opt" ];
     runScript = "/opt/zoom/ZoomLauncher";