Remove getPlatformLocale test

This test doesn't pass on systems that do not have a locale.
diff --git a/test/usage_impl_io_test.dart b/test/usage_impl_io_test.dart
index a0f3494..a150249 100644
--- a/test/usage_impl_io_test.dart
+++ b/test/usage_impl_io_test.dart
@@ -41,10 +41,6 @@
   });
 
   group('usage_impl_io', () {
-    test('getPlatformLocale', () {
-      expect(getPlatformLocale(), isNotNull);
-    });
-
     test('getDartVersion', () {
       expect(getDartVersion(), isNotNull);
     });