streets and street_labels inconsistent of link kind values

[pnorman]

trafficstars

a highway=motorway_link gets kind=motorway link=true in the streets layer, while in the street_label layer it gets kind=motorway_link. This is inconsistent and makes it more confusing to write styles.

[CommanderStorm]

If the spec is read stringtly, the kind is

Feature class, contains value of highway=* , aeroway=* or railway=*

The kind for the streets layer is just coalesces these.

Since motorway_link is not one of the kinds listed below, it should get filtered out.

Menaning, if the spec is pedantically followed, the link property can never ever be true.

Planetiler handles this by stripping the _link part from the kind.