Cleanup url saved object mappings (#153832)

## Summary

Partially addresses #153484 for
the url saved object.

For reviewers: The attributes are still accessible through SO
`.attributes`, it is just ES mappings are not created anymore.

src/core/server/integration_tests/saved_objects/migrations/group2/check_registered_types.test.ts

@@ -148,7 +148,7 @@ describe('checking migration metadata changes on all registered SO types', () =>
         "upgrade-assistant-reindex-operation": "09ac8ed9c9acf7e8ece8eafe47d7019ea1472144",
         "uptime-dynamic-settings": "9a63ce80904a04be114749e426882dc3ff011137",
         "uptime-synthetics-api-key": "599319bedbfa287e8761e1ba49d536417a33fa13",
-        "url": "292ec2e6816bf2d7c16a96e800c7ff564b002b52",
+        "url": "816fa15bfe460ce39108ed8095e60fdbfcc40f11",
         "usage-counters": "f478b2668be350f5bdc08d9e1cf6fbce0e079f61",
         "visualization": "55530e57ffe86bfd7c2a2b50461398c1f7a99e95",
         "workplace_search_telemetry": "10e278fe9ae1396bfc36ae574bc387d7e696d43f",

src/plugins/share/server/url_service/saved_objects/register_url_service_saved_object_type.ts

@@ -47,32 +47,12 @@ export const registerUrlServiceSavedObjectType = (
             },
           },
         },
-        accessCount: {
-          type: 'long',
-        },
         accessDate: {
           type: 'date',
         },
         createDate: {
           type: 'date',
         },
-        // Legacy field - contains already pre-formatted final URL.
-        // This is here to support old saved objects that have this field.
-        // TODO: Remove this field and execute a migration to the new format.
-        url: {
-          type: 'text',
-          fields: {
-            keyword: {
-              type: 'keyword',
-              ignore_above: 2048,
-            },
-          },
-        },
-        // Information needed to load and execute a locator.
-        locatorJSON: {
-          type: 'text',
-          index: false,
-        },
       },
     },
     migrations: () => {