Fix telemetry CLI to write empty properties collection (elastic#205746)

Follow-up of elastic#205613. Remove check blocking empty properties from
writing.

Author: dokmic

packages/kbn-telemetry-tools/src/tools/tasks/write_to_file_task.ts

@@ -15,7 +15,7 @@ export function writeToFileTask({ roots }: TaskContext) {
   return roots.map((root) => ({
     task: async () => {
       const fullPath = path.resolve(process.cwd(), root.config.output);
-      if (root.mapping && Object.keys(root.mapping.properties).length > 0) {
+      if (root.mapping) {
         // Sort first-level properties alphabetically
         root.mapping.properties = Object.fromEntries(
           Object.entries(root.mapping.properties).sort(([a], [b]) => {

x-pack/platform/plugins/private/telemetry_collection_xpack/schema/xpack_plugins.json

@@ -1,4 +1,3 @@
 {
-  "properties": {
-  }
+  "properties": {}
 }