Fix socialite provider

[hermesdj]

Latest version of Socialite (https://github.com/laravel/socialite/releases/tag/v5.12.0) added a breaking bug for EVE authentication with this PR : laravel/socialite#684

The fix is to change the list of fields sent in the form body to the token endpoint to no longer include client_id and client_secret because they are provided in the Authorization header. This is the "correct" way to provide client_id/client_secret to an OAuth endpoint (that was the point of the PR on socialite in the first place). So the fix I propose is to accept this behavior and only remove the unecessary fields from the form body.

The Original SeAT error was :

Client error: `POST https://login.eveonline.com/v2/oauth/token` resulted in a `400 Bad Request` response:
{"error":"invalid_request","error_description":"Client credentials should only be provided once. Remove them from either (truncated...)

meaning the client_id/client_secret combo should be in the Authorization header OR the form body, but not both.