[TOOL-2810] Remove unused assets from dashboard (#5813)

## Problem solved

Short description of the bug fixed or feature added

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## PR-Codex overview
This PR focuses on the removal of various asset files from the `apps/dashboard/public/assets` directory, including images and templates related to contracts, icons, and landing pages.

### Detailed summary
- Deleted the following files:
  - `add-contract/drop.png`
  - `tw-icons/nft-drop.png`
  - `templates/nft-drop.png`
  - `templates/tappyfowl.png`
  - `templates/unity-iap.png`
  - `templates/cat-attack.png`
  - `templates/mintcaster.png`
  - `tw-icons/marketplace.png`
  - `templates/marketplace.png`
  - `templates/nft-gallery.png`
  - `landingpage/white-logo.png`
  - `templates/expo-starter.png`
  - `templates/next-starter.png`
  - `templates/node-starter.png`
  - `templates/thirdweb-eth.png`
  - `templates/vite-starter.png`
  - `landingpage/marketplace.png`
  - `templates/unity-pioneer.png`
  - `templates/web3-warriors.png`
  - `add-contract/marketplace.png`
  - `templates/nft-gated-site.png`
  - `templates/unity-take-flight.png`
  - `templates/unity-blockventure.png`
  - `templates/phygital-experience.png`
  - `solutions-pages/gaming/marketplace.png`

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