Removed api:versions from config

refs: https://github.com/TryGhost/Toolbox/issues/229

- Removed the final usage (logging only) of config.get('api:versions') and removed the config
- This is one of the last references to API versioning in the codebase & we don't need it anymore
- Cleaned up a random comment whilst searching for refs

core/boot.js

@@ -252,9 +252,6 @@ async function initDynamicRouting() {
 async function initServices({config}) {
     debug('Begin: initServices');
 
-    const defaultApiVersion = config.get('api:versions:default');
-    debug(`Default API Version: ${defaultApiVersion}`);
-
     debug('Begin: Services');
     const stripe = require('./server/services/stripe');
     const members = require('./server/services/members');

core/server/services/url/config.js

@@ -3,8 +3,6 @@
  * They contain minimum filters for public accessibility of resources.
  */
 
-// @TODO: keep this similar to ./v4.js until the v5 release
-
 module.exports = [
     {
         type: 'posts',

core/shared/config/overrides.json

@@ -77,32 +77,6 @@
     "maintenance": {
         "enabled": false
     },
-    "api": {
-        "versions": {
-            "all": ["v2", "v3", "v4", "v5", "canary"],
-            "default": "v4",
-            "canary": {
-                "admin": "canary/admin",
-                "content": "canary/content"
-            },
-            "v5": {
-                "admin": "admin",
-                "content": "content"
-            },
-            "v4": {
-                "admin": "v4/admin",
-                "content": "v4/content"
-            },
-            "v3": {
-                "admin": "v3/admin",
-                "content": "v3/content"
-            },
-            "v2": {
-                "admin": "v2/admin",
-                "content": "v2/content"
-            }
-        }
-    },
     "imageOptimization": {
         "defaultMaxWidth": 2000,
         "contentImageSizes": {