fix:removing mintlify images (#181)

### TL;DR

Removed unused image files from the mintlify directory.

### What changed?

Deleted three image files that were no longer needed:
- `mintlify/images/checks-passed.png`
- `mintlify/images/hero-dark.png`
- `mintlify/images/hero-light.png`

### How to test?

Verify that these images are not referenced anywhere in the codebase and that their removal doesn't affect any UI components or documentation.

### Why make this change?

Cleaning up unused assets to reduce repository size and remove clutter. These images were likely leftover from previous documentation or UI designs that are no longer in use.

Author: pengying