Remove release files from repo directory

[DusKing1]

As we introduced the GitHub Action to do the CI job, we can use automatically generated firmware to release.

This is the first step of moving to use GitHub's native release system to do the release.

I did this for several reasons:

• those .hex .bin and config tools in the release folder need to be download when you using the git command to down this repo. This is quite slow for our devs in Asia.
• GitHub's release system can also produce permanent links so for the blheli-configurator to use, and its link is a little bit shorter than repo folder

Oh, and I also delete the config tools because I think it should be moved to other link or repo

Might breaks blheli-configurator's flashing system for now. What do you think about this change @mikeller

[ColinNiu]

It's definitely good news to me if we can achieve this, it's really a pain cloning/fetching this repo. And:

1. About the config tool and bootloader, maybe we can create a dedicated tool release, upload tools there, and give the static url in the README;
2. Release should contain official binary only. For those who want to taste the latest (and pr) features but unwilling to build from source code locally, action artifacts are their choice. This can also be mentioned in the README.

[DusKing1]

There's a second way to help who wanna taste dev build: create a nightly build repo, and push artifacts to there, like how betaflight does their dev builds.