tests/yubikey-agent: reorganize darwin and linux

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

tests/modules/services/yubikey-agent-darwin/default.nix

@@ -1,5 +0,0 @@
-{ lib, pkgs, ... }:
-
-lib.optionalAttrs pkgs.stdenv.hostPlatform.isDarwin {
-  yubikey-agent-darwin = ./service.nix;
-}

tests/modules/services/yubikey-agent/darwin/default.nix

@@ -0,0 +1,3 @@
+{
+  yubikey-agent = ./service.nix;
+}

tests/modules/services/yubikey-agent/default.nix

@@ -1,5 +1,3 @@
 { lib, pkgs, ... }:
-
-lib.optionalAttrs pkgs.stdenv.hostPlatform.isLinux {
-  yubikey-agent = ./service.nix;
-}
+(lib.optionalAttrs pkgs.stdenv.hostPlatform.isDarwin (import ./darwin/default.nix))
+// (lib.optionalAttrs pkgs.stdenv.hostPlatform.isLinux (import ./linux/default.nix))

tests/modules/services/yubikey-agent/linux/default.nix

@@ -0,0 +1,3 @@
+{
+  yubikey-agent = ./service.nix;
+}