[Tech Debt] Update E2E setup for Exploratory View app

[CoenWarmer]

Part of #152783

📝 Summary

The Synthetics team placed an E2E testing solution inside the Observability app called Microsoft Playwright. They used that solution to test the Exploratory View route that they maintained inside the Observability app.

As the Exploratory View app has been moved into its own separate app (together with Playwright to test it), and the Actionable Observability team only uses Selenium FTR tests for its E2E testing needs, it makes sense to remove Playwright from the Observability app.

✅ Acceptance criteria

• All traces of Playwright inside the Observability app and CI configuration should be removed

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)