[Fix] Replace koa-remove-trailing-slashes with inhouse script

Created by: daikei

Once again, I'm looking to remove another 5kb package, replacing it with an in-house script. this removes 5kb worth of data, translating it to a 206 byte script that gets the job done.

I'd also like to mention that in it's past, koa-remove-trailing-past has been associated with an Open Redirect CVE; that, and the package is complete overkill for the task it's trying to accomplish.