Remove the leading "mapbox://" from the default MapBox style URL,
as it now seems to break the resulting generated tile URLs in
QtLocation. I suspect this is related to the HTTPS support that
was added in Qt 5.12.
Bug-AGL: SPEC-3837
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ib5bfe75a2e741b10791260c408dedfee1dbd60cb