add icons to kerb fields, tweak label, drop from specialized presets

specialized presets should be switched using the preset selector, no need to duplicate that as a combo box. this effectively reverts https://github.com/openstreetmap/iD/issues/6360

(re icons, see also https://github.com/openstreetmap/id-tagging-schema/pull/1077#issuecomment-1966247784)

also remove duplicates of translatable strings

data/fields/kerb.json

@@ -29,5 +29,11 @@
                 "description": "Some sort of curb is present at this location, unknown whether it is raised, lowered, flush etc."
             }
         }
+    },
+    "icons": {
+        "raised": "temaki-kerb-raised",
+        "lowered": "temaki-kerb-lowered",
+        "flush": "temaki-kerb-flush",
+        "rolled": "temaki-kerb-rolled"
     }
 }