Fix QR code scanner layout in "Pair devices over Wi-Fi" page.

The toolbar needs to be disabled to remove the empty space at the top
of the page. Also added the landscape layout xml.

Bug: 193602141
Test: atest SettingsUnitTests and manual

Change-Id: I30368835979b360a8f09e16f70adf57064784517
(cherry picked from commit fd009229)