t1utils: set meta.platforms = all

Suggested by @sjourdois on github, to allow building on darwin.

pkgs/tools/misc/t1utils/default.nix

···
     # README from tarball says "BSD-like" and points to non-existing LICENSE
     # file...
     license = "Click"; # MIT with extra clause, https://github.com/kohler/t1utils/blob/master/LICENSE
-    platforms = platforms.linux;
+    platforms = platforms.all;
     maintainers = [ maintainers.bjornfor ];
   };
 }