feat: improving verification key generation (#1050)

## What ❔

* Removed vk_generator.rs that was no longer used
* Added more logging to VK generation
* Added an early check to detect if CRS file is missing

## Why ❔

* vk_generator logic code is already present in witness_generator crate
* more logging helps to see what is happening
* early check saves people 30 minutes, if they didn't configure their
setup correctly.