Fix theme for package uninstall dialog

Previous default was using light whereas
Wear requires dark. Updated alert dlg theme
for consistency.

Bug: b/327483294
Test: adb shell am start -n
    com.google.android.packageinstaller/com.android.packageinstaller.UninstallerActivity
    -d <package>
Change-Id: I7079325a573935a5136997cfb4aa3b45c4673dc2