some refactoring

modules/options/monitors/default.nix

@@ -14,10 +14,6 @@ in {
             type = types.str;
             example = "DP-1";
           };
-          primary = mkOption {
-            type = types.bool;
-            default = false;
-          };
           width = mkOption {
             type = types.int;
             example = 1920;
@@ -60,14 +56,4 @@ in {
     );
     default = [];
   };
-  config = {
-    assertions = [
-      {
-        assertion =
-          ((lib.length config.monitors) != 0)
-          -> ((lib.length (lib.filter (m: m.primary) config.monitors)) == 1);
-        message = "Exactly one monitor must be set to primary.";
-      }
-    ];
-  };
 }