tests: no longer load libnss_{files|dns}

Those libraries aren't provided by systemd so they shouldn't be
included here

src/test/test-nss-hosts.c

@@ -420,7 +420,7 @@ static int parse_argv(int argc, char **argv,
 #if ENABLE_NSS_MYMACHINES
                                 "mymachines",
 #endif
-                                "dns");
+                                NULL);
         assert_se(modules);
 
         if (argc > 2) {

src/test/test-nss-users.c

@@ -214,7 +214,7 @@ static int parse_argv(int argc, char **argv,
 #if ENABLE_NSS_MYMACHINES
                                 "mymachines",
 #endif
-                                "files");
+                                NULL);
         assert_se(modules);
 
         if (argc > 2)