~/.ssh/config block breaking access to GitHub

I ran into this issue yesterday:
> I'm having SSH issues now and I can't clone the repo. I could earlier today but I was on a poor connection and submodules weren't downloading properly. Got back home and was getting errors trying to resume downloads. So, I deleted the directory and started again. Now I'm getting this error:
> ```
> ssh_exchange_identification: Connection closed by remote host
> fatal: Could not read from remote repository.
> 

> Please make sure you have the correct access rights
> and the repository exists.
> ```
> I can see the repo fine in the browser. Strange thing is, I'm getting this even on public repos. Some config has broken somewhere I think.

While troubleshooting, I noticed my ~/.ssh/config file was last updated yesterday around the time I was having the issues with submodules. The following block was repeated about ten times in the file:
```
##
Host github.com
User git
ProxyCommand nc -x localhost:9050 %h %p
##
```
Emptying the file fixed the GitHub issue. It didn't occur to me that proxy might have been the issue, as everything else was working normally and I've been at home since.

I don't know if this is specifically something that needs fixing or if it's a rare edge case, but thought I'd write it up incase anyone else runs into the issue.