Hide the accessibility location preference when gesture navigation mode enabled.

If it's grey out, users don't have the alternative way in that page to enable it. According to the UX design, we should hide it if it is needed.

Bug: 186776534
Test: make RunSettingsRoboTests -j52 ROBOTEST_FILTER=AccessibilityButtonLocationPreferenceControllerTest
Change-Id: If2f659da32345938e2930fde42365cd796571068