How to downgrade Google search app in recovery?
some applications are in deferent locations, system/app holds certain applications while system/priv-app holds other's... sometimes your phone provider also puts apps in system/vendor/operator/APP_FOLDERS_BY_NAME   and custom/app/   

These locations change depending on device, but mostly stick to the same root directory's..   


system/app
system/priv-app
system/vendor/
custom/


Just have a look around at the different sub folders, and i think it's inconveniently named something completely different, like Velvet.apk