Remove assets.yaml (radius-project#7832)

# Description

Cleaning up disabled workflow assets.yaml.

## Type of change
- This pull request is a minor refactor, code cleanup, test improvement,
or other maintenance task and doesn't change the functionality of Radius
(radius-project#7800 ).

Fixes: radius-project#7800
Signed-off-by: Reshma Abdul Rahim <[email protected]>