[Observability Onboarding] Remove legacy team ownership (elastic#203808)

## 📓 Summary

The @elastic/obs-ux-onboarding-team is a subset of the wider
@elastic/obs-ux-logs-team, which share the same ownership of the
onboarding plugins.

To reduce the noise and limitations around required team reviews and
pings, we'll remove the onboarding team and leave the logs team as the
unique owner of the onboarding, where these same engineers will cover
its maintenance.

Co-authored-by: Marco Antonio Ghiani <[email protected]>

Author: tonyghiani

.github/CODEOWNERS

@@ -938,8 +938,8 @@ x-pack/plugins/observability_solution/logs_shared @elastic/obs-ux-logs-team
 x-pack/plugins/observability_solution/metrics_data_access @elastic/obs-ux-infra_services-team
 x-pack/plugins/observability_solution/observability @elastic/obs-ux-management-team
 x-pack/plugins/observability_solution/observability_logs_explorer @elastic/obs-ux-logs-team
-x-pack/plugins/observability_solution/observability_onboarding @elastic/obs-ux-logs-team @elastic/obs-ux-onboarding-team
-x-pack/plugins/observability_solution/observability_onboarding/e2e @elastic/obs-ux-logs-team @elastic/obs-ux-onboarding-team
+x-pack/plugins/observability_solution/observability_onboarding @elastic/obs-ux-logs-team
+x-pack/plugins/observability_solution/observability_onboarding/e2e @elastic/obs-ux-logs-team
 x-pack/plugins/observability_solution/observability_shared @elastic/observability-ui
 x-pack/plugins/observability_solution/profiling @elastic/obs-ux-infra_services-team
 x-pack/plugins/observability_solution/profiling_data_access @elastic/obs-ux-infra_services-team

x-pack/plugins/observability_solution/observability_onboarding/e2e/kibana.jsonc

@@ -1,10 +1,7 @@
 {
   "type": "test-helper",
   "id": "@kbn/observability-onboarding-e2e",
-  "owner": [
-    "@elastic/obs-ux-logs-team",
-    "@elastic/obs-ux-onboarding-team"
-  ],
+  "owner": ["@elastic/obs-ux-logs-team"],
   "group": "observability",
   "visibility": "private",
   "devOnly": true

x-pack/plugins/observability_solution/observability_onboarding/kibana.jsonc

@@ -1,10 +1,7 @@
 {
   "type": "plugin",
   "id": "@kbn/observability-onboarding-plugin",
-  "owner": [
-    "@elastic/obs-ux-logs-team",
-    "@elastic/obs-ux-onboarding-team"
-  ],
+  "owner": ["@elastic/obs-ux-logs-team"],
   "group": "observability",
   "visibility": "private",
   "plugin": {