Delete `Accept` header is not checked for compliance with JSON:API

[lindyhopchris]

When fixing #184 I've realised there's no checking of the Accept media type in the destroy controller action. The JSON:API specification shows that a DELETE request should have an Accept: application/vnd.api+json header, as shown in this example:
https://jsonapi.org/format/#crud-deleting

We need to add this, however I'd consider this a breaking change - because at the moment people may have set up clients to not send the Accept header. So this should be fixed for 3.0.

[lindyhopchris]

This is done, issue will close when 3.x is merged to develop.

[lindyhopchris]

Closing this as 3.0 will be tagged soon for Laravel 10.