Does anyone know how to get rid of the small button on the navigation bar?

At one period I would have my nav bar auto hid in fullscreen apps but for some reason it stopped doing that. A cursory search on Google had me follow a few instructions to find how to return my phone back to normal.

However the option it provided me was to turn on the tiny little button in the left side of the nav bar to double click it to hid the bar.

The problem lies within that button, I never had that option turned on to hide my nav bar. Now suddenly I have to have a button that does nothing after it has been double pressed in order to have my bar hidden. I therefore no longer need the tiny button. Is there a way to return my phones design to its former glory?

If I'm understanding your question:
Settings, Display, Navigation Bar. It sounds like currently it is turned on. I think turning it off will fix it.