fixes for heads up
Revert "settings: Enable location mode header switch"

This reverts commit b6e2d0f0b29949091061ae8f3e524a1b82f59693.
Remove SystemSettingSwitchPreference
Hide heads up settings and show a notice if heads up is disabled.

This follows a UI pattern used at several other places, such as
daydream, screencast, profiles or blacklist settings.
Settings: Fix switch state being out of sync.

    - Since QS Tile can also set state of Heads up now,
    we have to set a content observer for the action bar
    switch.

Change-Id: I1c63fd2627a0f823eb6982456e1ed79ab84d1957