ZoomControllerBrowserTest.SettingsZoomAfterSigninWorks was used to test that the ZoomController updated its HostZoomMap subscription when a navigation across StoragePartitions occurred. This was introduced in crrev.com/c7bcb77d7708a5790933890686b3da059dac041b . This was made obsolete  by crrev.com/5f5bb820bb248b8ba47a53d60aefb85ca19ffb80 which changed the signin page to use a webview. The embedder now uses the default StoragePartition.

Currently, nothing navigates across StoragePartitions by design, but future isolation work may need the ability to navigate between StoragePartitions. So, we'll leave the associated logic as is and just remove the test.