Hide nav arrows by default

## What does this MR do?
- Fixes the arrow icon flashing on page load
- Removes settings dropdown at higher breakpoint
- Removes unneeded CSS

Closes #18941

## Screenshots (if relevant)
Arrow flashing bug:
![icon](/uploads/3db95626acd0adb37438bdbc2c4aa154/icon.gif)

Settings dropdown breaking nav:
<img src="/uploads/4351035f4cf8cb9fd892b621e6339e50/Screen_Shot_2016-06-21_at_4.25.50_PM.png" width="800px">

@alfredo1 would you mind double checking this to make sure the arrow flashing is definitely not happening?

See merge request !4843