Remove stale fields from example bblock.json files

Drop dateOfLastChange (no longer required), maturity, and scope, which
are not part of the current bblock metadata schema.

Author: avillar

_sources/myFeature/bblock.json

@@ -6,15 +6,12 @@
   "itemClass": "schema",
   "register": "ogc-building-block-examples",
   "version": "1.0",
-  "dateOfLastChange": "2023-05-19",
   "sources": [
     {
       "title": "OGC API - Features, Part 1, 7.16.2: Feature Response",
       "link": "https://docs.ogc.org/is/17-069r3/17-069r3.html#_response_7"
     }
   ],
-  "maturity": "development",
-  "scope": "unstable",
   "dependsOn": [
   ],
   "tags": [

_sources/mySchema/bblock.json

@@ -7,15 +7,12 @@
   "itemClass": "schema",
   "register": "ogc-building-block-register",
   "version": "0.1",
-  "dateOfLastChange": "2023-04-05",
   "link": "https://github.com/opengeospatial/bblock-template",
   "sources": [
     {
       "title": "Sample source document",
       "link": "https://example.com/sources/1"
     }
   ],
-  "maturity": "mature",
-  "scope": "unstable",
   "tags": ["templates"]
 }