EGL/TopCanvas: fix build breakage

Build was broken after the PixelSize transition.
Engine/Task/Ordered/Points: Always use arrival safety height

Before this change terrain safety height was always used for intermediate
task waypoint arrival height calculations. Every other arrival height
displayed by xcsoar uses the arrival safety height. This difference could
lead to potential dangerous situations, e.g. when a pilot has a landable
as an intermediate task waypoint, as the arrival height is calculated
with different - and in the default configuration lower - margins.

Now the arrival safety height is always used for all task waypoints so
users don't need intimate knowledge of xcsoars internals to make sense
of them.