Clean up RLS Tester artifacts (#47866)

## Context

As per PR title - we're pausing the development of the RLS Tester
feature preview while we re-evaluate its direction. Have also updated
the GH discussion
[here](https://github.com/orgs/supabase/discussions/45233) RE this! 🙏

Removes the RLS Tester UI + Sandbox functionality

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Removed Features**
* Removed the RLS Tester feature preview, banner, and database policy
testing workflow.
* The related SQL testing, role selection, policy summaries, sandbox
management, and result views are no longer available.
* **Bug Fixes**
* Improved accessibility on the database policies page by adding a label
to the clear-filter button.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/studio/package.json

@@ -51,8 +51,6 @@
     "@dnd-kit/modifiers": "^9.0.0",
     "@dnd-kit/sortable": "^8.0.0",
     "@dnd-kit/utilities": "^3.2.2",
-    "@electric-sql/pglite": "0.4.5",
-    "@electric-sql/pglite-tools": "^0.3.4",
     "@graphiql/react": "^0.37.3",
     "@graphiql/toolkit": "^0.11.3",
     "@hcaptcha/react-hcaptcha": "^1.12.0",