[DASH-639] Remove unused assets (#5759)

## Problem solved

Short description of the bug fixed or feature added

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## PR-Codex overview
This PR focuses on the deletion of numerous asset files from the `apps/dashboard/public/assets` directory, which includes images related to partners, ambassadors, landing pages, grants, and startup programs.

### Detailed summary
- Deleted multiple image files from `apps/dashboard/public/assets/partners`
- Removed various ambassador-related images from `apps/dashboard/public/assets/ambassadors`
- Cleared out several landing page images from `apps/dashboard/public/assets/landingpage`
- Eliminated images associated with grants and startup programs from `apps/dashboard/public/assets/grant` and `apps/dashboard/public/assets/startup-program` respectively
- Removed community and product page images from the respective directories

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