Render administrative boundary text labels for relations only (#3762)

* Render text labels along borders of admin boundary relations only

Currently lines are only rendered for borders mapped as relations (i.e. osm_id <0) but the text labels along the borders are rendered for relations and closed ways. This commit adds a filter for "AND osm_id < 0" to the admin-text layer, so that the text labels do not appear in the rare occasions when an administrative boundary is mapped as a closed way instead of a relation

* Render central name labels for country and province/state relations only

project.mml

@@ -1191,6 +1191,7 @@ Layer:
             AND admin_level = '2'
             AND name IS NOT NULL
             AND way_area > 100*!pixel_width!::real*!pixel_height!::real
+            AND osm_id < 0
           ORDER BY way_area DESC
         ) AS country_names
     properties:
@@ -1234,6 +1235,7 @@ Layer:
             AND admin_level = '4'
             AND name IS NOT NULL
             AND way_area > 100*!pixel_width!::real*!pixel_height!::real
+            AND osm_id < 0
           ORDER BY way_area DESC
         ) AS state_names
     properties:
@@ -2100,6 +2102,7 @@ Layer:
           WHERE boundary = 'administrative'
             AND admin_level IN ('1', '2', '3', '4', '5', '6', '7', '8', '9', '10')
             AND name IS NOT NULL
+            AND osm_id < 0
           ORDER BY admin_level::integer ASC, way_area DESC
         ) AS admin_text
     properties: