I have already tried options mentioned in many other answers here/ posts online. I have a nexus 5
disable google now: option is disabled
use custom launcher: shows even in Nova launcher!
Edit: here is what I tried:
https://www.androidpit.com/how-to-remove-the-google-search-bar-from-your-android-homescreen
it doesn't work because Google Search doesn't appear in the list of installed apps in marshmallow