fix inline comment that can cause deface errors

see https://github.com/spree/deface/issues/113 for more info

when using deface to make changes to app/views/spree/admin/payment_methods/_form.html.erb I encounter the following error:

```text
syntax error, unexpected '<', expecting keyword_end
```

I tracked it down to the inline comment issue discussed in https://github.com/spree/deface/issues/113