Remove fetchMD5warn

Deprecation warnings should not be used in Nixpkgs because they spam
innocent "nix-env -qa" users with (in this case) dozens of messages
that they can't do anything about.

This also reverts commit 2ca8833383.

pkgs/top-level/make-tarball.nix

@@ -63,15 +63,12 @@ releaseTools.sourceTarball rec {
     fi
 
     # Check that all-packages.nix evaluates on a number of platforms without any warnings.
-    # Filter out MD5 warnings for now
     for platform in i686-linux x86_64-linux x86_64-darwin; do
         header "checking Nixpkgs on $platform"
 
         NIXPKGS_ALLOW_BROKEN=1 nix-env -f . \
             --show-trace --argstr system "$platform" \
-            -qa --drv-path --system-filter \* --system 2>&1 >/dev/null |
-            (grep -v '^trace: INFO: Deprecated use of MD5 hash in fetch' || true) |
-            tee eval-warnings.log
+            -qa --drv-path --system-filter \* --system 2>&1 >/dev/null | tee eval-warnings.log
 
         if [ -s eval-warnings.log ]; then
             echo "Nixpkgs on $platform evaluated with warnings, aborting"