Revert "astroid: require notmuch synchronize flags"

The Astroid program can work without this option,
which should be disabled when synchronising emails with muchsync for example.

This reverts commit fa3d1f98e0.

(cherry picked from commit 24dbac8da7)

modules/programs/astroid.nix

@@ -106,14 +106,6 @@ in
   };
 
   config = mkIf cfg.enable {
-    assertions = [
-      {
-        assertion = config.programs.notmuch.maildir.synchronizeFlags;
-        message = "The astroid module requires"
-          + " 'programs.notmuch.maildir.synchronizeFlags = true'.";
-      }
-    ];
-
     home.packages =  [ pkgs.astroid ];
 
     xdg.configFile."astroid/config".source =