Remove unused envs from dashboard .env.example (#5209)

## Problem solved

Short description of the bug fixed or feature added

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## PR-Codex overview
This PR focuses on updating the `.env.example` file for the `dashboard` application by removing deprecated or unnecessary environment variable entries.

### Detailed summary
- Removed the comment regarding `PAYMENTS_ADMIN_SECRET` and its associated empty value.
- Deleted the line to disable telemetry (`NEXT_TELEMETRY_DISABLED`).
- Removed the comment and empty value for `NEXT_PUBLIC_TRENCH_2_API_ENDPOINT`.

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apps/dashboard/.env.example

@@ -75,15 +75,6 @@ GITHUB_API_TOKEN="ghp_..."
 # Upload server url
 NEXT_PUBLIC_DASHBOARD_UPLOAD_SERVER="https://storage.thirdweb-preview.com"
 
-# Payments Admin Secret. For dev, get this value from paper-web-dev (on Zeet)'s "HASURA_ADMIN_SECRET_KEY" env var
-PAYMENTS_ADMIN_SECRET=""
-
-# Disable telemetry
-NEXT_TELEMETRY_DISABLED=1
-
-# Use trench for KYC
-NEXT_PUBLIC_TRENCH_2_API_ENDPOINT=""
-
 # Unthread variables - only required for submitting the support form in /support
 UNTHREAD_API_KEY=""
 UNTHREAD_TRIAGE_CHANNEL_ID=""