parking/orientation: update and deprecate key (#673)

Following the successful street parking revision proposal https://wiki.openstreetmap.org/wiki/Proposed_features/street_parking_revision#Summary:_What_is_proposed,_changed_and_deprecated? the tag for orientation on separately mapped parking spaces is now just `orientation`.

data/fields/orientation/orientation_parking.json

@@ -1,5 +1,5 @@
 {
-    "key": "parking:orientation",
+    "key": "orientation",
     "type": "combo",
     "label": "Orientation",
     "strings": {