simplify post box preset

dropping the GB regional variant in favour of making the `royal_cypher` field regional.

see also https://github.com/ideditor/schema-builder/issues/94

data/fields/royal_cypher-GB.json

@@ -16,5 +16,10 @@
         }
     },
     "autoSuggestions": false,
-    "customValues": false
+    "customValues": false,
+    "locationSet": {
+        "include": [
+            "gb"
+        ]
+    }
 }

data/presets/amenity/post_box.json

@@ -3,7 +3,9 @@
     "fields": [
         "operator",
         "collection_times",
-        "ref"
+        "ref",
+        "post_box/type-GB",
+        "royal_cypher-GB"
     ],
     "moreFields": [
         "access_simple",
@@ -46,7 +48,6 @@
     ],
     "locationSet": {
         "exclude": [
-            "gb",
             "us"
         ]
     },

data/presets/amenity/post_box/post_box-GB.json

@@ -1,25 +0,0 @@
-{
-    "icon": "temaki-post_box",
-    "locationSet": {
-        "include": [
-            "gb"
-        ]
-    },
-    "fields": [
-        "{amenity/post_box}",
-        "post_box/type-GB",
-        "royal_cypher"
-    ],
-    "moreFields": [
-        "{amenity/post_box}",
-        "drive_through"
-    ],
-    "geometry": [
-        "point",
-        "vertex"
-    ],
-    "tags": {
-        "amenity": "post_box"
-    },
-    "name": "{amenity/post_box}"
-}