Fix Error 400 Bad Request on API call

I was running into the same issue as mentioned at https://easydigitaldownloads.com/support/topic/error-400-bad-request-on-api-call/

License key activation does not work if you include the `$params` in the request body of a `wp_remote_get()` call. You get a 400 bad request.

By removing this line, the license activation is successful.