Dark theme drop down does not show selected option

a place holder for the summary was updated in commit https://googleplex-android-review.git.corp.google.com/changes/platform%2Fpackages%2Fapps%2FSettings~9818614/revisions/3/files/res%2Fxml%2Fdark_mode_settings.xml/download?parent=1
This change is reverted in this CL

Test: manual
Fixes: 145672617
Change-Id: I41443e7334487e3afac0343333a9ed289d2fe390