docs: Remove confusing comment from boto example.

The boto config file format should have comments on a separate line.

here is the docs:

http://boto.cloudhackers.com/en/latest/boto_config_tut.html#details

docs/production/upload-backends.md

@@ -43,9 +43,11 @@ created (e.g. `exampleinc-zulip-uploads`).
     ```
     [s3]
     use-sigv4 = True
-    host = s3.eu-central-1.amazonaws.com  # Substitute your AWS region here
+    # Edit to provide your S3 bucket's AWS region here.
+    host = s3.eu-central-1.amazonaws.com
     ```
 
+
 1. You will need to configure `nginx` to direct requests for uploaded
     files to the Zulip server (which will then serve a redirect to the
     appropriate place in S3), rather than serving them directly.