Use the same logic to create navigation bars(1/2)

By ag/5368441, we can have TYPE_NAVIGATION_BAR per display now.
We don't need the hacking NAVIGATION_BAR_PANEL anymore.

Bug: 117478341
Test: atest SystemUiTests
Test: atest ActivityManagerMultiDisplayTests
Change-Id: Ic43f472e3b56d3981c813e8ca29f59e2d1c481cc