[ES 9.0] Remove body workaround (@elastic/obs-ux-management-team) (#217223)

## Summary

Follow up to #213375: The latest
version of the ES client fixed the issue
elastic/elasticsearch-js#2584.

We should be able to remove all usages of `// @ts-expect-error
[email protected]
https://github.com/elastic/elasticsearch-js/issues/2584`.

Author: afharo

x-pack/solutions/observability/plugins/observability/server/utils/create_or_update_index.ts

@@ -91,7 +91,6 @@ function updateExistingIndex({
 }) {
   return client.indices.putMapping({
     index,
-    // @ts-expect-error [email protected] https://github.com/elastic/elasticsearch-js/issues/2584
-    body: mappings,
+    ...mappings,
   });
 }