lib.systems.equals: use lib imports instead of builtins (#507317)

lib/systems/default.nix

@@ -3,11 +3,11 @@
 let
   inherit (lib)
     any
-    filterAttrs
+    attrNames
+    filter
     foldl
     hasInfix
     isAttrs
-    isFunction
     isList
     mapAttrs
     optional
@@ -43,9 +43,8 @@ let
   */
   equals =
     let
-      # perf: avoid lib.isFunction because system attrs are never __functor-style attrsets.
-      removeFunctions =
-        a: removeAttrs a (builtins.filter (n: builtins.isFunction a.${n}) (builtins.attrNames a));
+      # System attrs are never __functor-style attrsets, so builtins.isFunction suffices.
+      removeFunctions = a: removeAttrs a (filter (n: builtins.isFunction a.${n}) (attrNames a));
     in
     a: b: removeFunctions a == removeFunctions b;