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. You get a 400 bad request. By removing this line, the license activation is successful.
Merge pull request #2340 from davekiss/patch-1

Fix Error 400 Bad Request on API call