treewide: Replace meta.available checks in shouldUsePackages copypasta

This reverts commit 79d8353b5e.

This sort of code breaks config.{allowBroken, allowUnsupportedSystem} =
true by making them do unpredictable things.

pkgs/tools/filesystems/ceph/generic.nix

@@ -37,7 +37,8 @@ with stdenv.lib;
 let
 
   shouldUsePkg = pkg_: let pkg = (builtins.tryEval pkg_).value;
-    in if pkg.meta.available or false then pkg else null;
+    in if lib.any (lib.meta.platformMatch stdenv.hostPlatform) pkg.meta.platforms
+      then pkg else null;
 
   optYasm = shouldUsePkg yasm;
   optFcgi = shouldUsePkg fcgi;