make-tarball.nix: Don't check broken packages

They're broken after all. In particular, this prevents us from
evaluating packages that are unsupported on a particular platform.

Reverts a147ddc42c.

Fixes #20817.

pkgs/top-level/make-tarball.nix

@@ -66,7 +66,7 @@ releaseTools.sourceTarball rec {
     for platform in i686-linux x86_64-linux x86_64-darwin; do
         header "checking Nixpkgs on $platform"
 
-        NIXPKGS_ALLOW_BROKEN=1 nix-env -f . \
+        nix-env -f . \
             --show-trace --argstr system "$platform" \
             -qa --drv-path --system-filter \* --system 2>&1 >/dev/null | tee eval-warnings.log
 
@@ -76,7 +76,7 @@ releaseTools.sourceTarball rec {
         fi
         rm eval-warnings.log
 
-        NIXPKGS_ALLOW_BROKEN=1 nix-env -f . \
+        nix-env -f . \
             --show-trace --argstr system "$platform" \
             -qa --drv-path --system-filter \* --system --meta --xml > /dev/null
         stopNest