emacsMacport: don't explicitly unpack the tarballs as gzip

tar's -z flag only works for gzip-compressed tarballs. When passed a tarball
compressed with a different compressor (like xz), tar will fail to extract it.

Since tar can auto-detect a compressed tarball and use the appropriate
decompressor itself since forever, this is unecessary now.

pkgs/applications/editors/emacs/macport.nix

@@ -37,11 +37,11 @@ stdenv.mkDerivation rec {
 
   postUnpack = ''
     mv $sourceRoot $name
-    tar xzf $macportSrc -C $name --strip-components=1
+    tar xf $macportSrc -C $name --strip-components=1
     mv $name $sourceRoot
 
     # extract retina image resources
-    tar xzfv $hiresSrc --strip 1 -C $sourceRoot
+    tar xfv $hiresSrc --strip 1 -C $sourceRoot
   '';
 
   postPatch = ''