Summary:
Per t34270005 we're changing all publicly hosted detectron assets to a new low-cost CDN-backed S3 bucket. The migration requires rewriting all instances of `https://s3-us-west-2.amazonaws.com/detectron` to `https://dl.fbaipublicfiles.com/detectron`.

This giant codemod does it.

```
cd fbcode

rg -l s3-us-west-2.amazonaws.com/detectron > ~/filelist.txt

for F in $(cat ~/filelist.txt);
  sed -i '' -e 's/s3-us-west-2\.amazonaws\.com\/detectron/dl.fbaipublicfiles.com\/detectron/g' $F
done
```

Reviewed By: jma127

Differential Revision: D13538734

fbshipit-source-id: 4fe5c797770b0d9f675cee53dbcb6b52857fa45d