when the kerb tag is used by iteslef, we can't assume it's a barrier

as it might also be an incompletely tagged crossing node

fixes #858

data/presets/barrier/kerb/flush.json

@@ -9,9 +9,6 @@
         "line"
     ],
     "tags": {
-        "kerb": "flush"
-    },
-    "addTags": {
         "barrier": "kerb",
         "kerb": "flush"
     },

data/presets/barrier/kerb/lowered.json

@@ -10,9 +10,6 @@
         "line"
     ],
     "tags": {
-        "kerb": "lowered"
-    },
-    "addTags": {
         "barrier": "kerb",
         "kerb": "lowered"
     },

data/presets/barrier/kerb/raised.json

@@ -10,9 +10,6 @@
         "line"
     ],
     "tags": {
-        "kerb": "raised"
-    },
-    "addTags": {
         "barrier": "kerb",
         "kerb": "raised"
     },

data/presets/barrier/kerb/rolled.json

@@ -10,9 +10,6 @@
         "line"
     ],
     "tags": {
-        "kerb": "rolled"
-    },
-    "addTags": {
         "barrier": "kerb",
         "kerb": "rolled"
     },