Fix comment in sync_user_settings_unittests.cc

I accidentally left in an old version of a comment.

TBR=treib@chromium.org

Bug: none
Change-Id: I6fdb1761e840b58e3fe76b9079343a094b7a2ee2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2104988Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750621}

components/sync/driver/sync_user_settings_unittest.cc

@@ -177,7 +177,6 @@ TEST_F(SyncUserSettingsTest, PreferredTypesNotKeepEverythingSynced) {
     // GetPreferredUserTypes() returns ModelTypes, which includes both browser
     // and OS types. However, this test exercises browser UserSelectableTypes,
     // so disable OS selectable types.
-    // This test only exercises browser types, so disable all OS types.
     sync_user_settings->SetSelectedOsTypes(/*sync_all_os_types=*/false,
                                            UserSelectableOsTypeSet());
   }