remove route_calculation setting, always use OSRM routing (#1064)

The per-user route_calculation toggle was a second, hidden on/off layer
on top of the day footer's show-route button, and made it easy to end up
with straight-line routes for no obvious reason. Drop the setting
entirely: routing is always on, the footer toggle stays the single
switch. Old stored values are simply ignored (settings are key-value, no
migration needed).

client/src/types.ts

@@ -215,7 +215,6 @@ export interface Settings {
   temperature_unit: string
   time_format: string
   show_place_description: boolean
-  route_calculation?: boolean
   blur_booking_codes?: boolean
   map_booking_labels?: boolean
   map_provider?: 'leaflet' | 'mapbox-gl'