Remove example - deep clean

[stevenhwu]

Check out https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/removing-sensitive-data-from-a-repository

I generally use Using the BFG

The example folder will break this repo.

It's huge in size and will be updated with more large files in the future. For now.

• [x] deep clean example folder, make sure it's not in the history
• [ ] migrate example to github LFS, deal with this later
• [x] use fastq.gz

[ShawnChen09]

i already tracked large files by git lts, isn't that enough?

[ShawnChen09]

i will convert fastq to fastq.gz later

[stevenhwu]

git track full history, check the size of .git