lib.systems.equals: optimize removeFunctions (#506578)

  */

  equals =

    let

      removeFunctions = a: filterAttrs (_: v: !isFunction v) a;

      # perf: avoid lib.isFunction because system attrs are never __functor-style attrsets.

      removeFunctions =

        a: removeAttrs a (builtins.filter (n: builtins.isFunction a.${n}) (builtins.attrNames a));

    in

    a: b: removeFunctions a == removeFunctions b;