Call static methods directly, no wrappers

There was some maintenance risk of signaure/type mismatches here,
and in a subsequent commit I'd have needed even more wrappers
around related methods in Grid.

Also removed IsochroneFeature which is unused, but called those
removed wrapper functions. IsochroneFeature was ported to JS as
Jsolines, and sees destination travel times as being located at
the top left corner of Mercator pixels. Removing it eliminates
a source of confusion if someone sees unused code doing this.