Remove unnecessary .env vars from setup instructions

`AWS_URL` and `AWS_POST_END_POINT` environment variables are now dynamically determined by the aws-sdk-php package.  Setting these to any value will make the sdk automatically assume you are using a custom endpoint and prevent the use of accelerator,

Author: kerkness

README.md

@@ -122,8 +122,6 @@ AWS_ACCESS_KEY_ID=
 AWS_SECRET_ACCESS_KEY=
 AWS_DEFAULT_REGION=
 AWS_BUCKET=
-AWS_URL="https://s3.amazonaws.com"
-AWS_POST_END_POINT="https://${AWS_BUCKET}.s3.amazonaws.com/"
 ```
 
 To allow direct multipart uploads to your S3 bucket, you need to add some extra configuration on bucket's `CORS configuration`.