Stop directly enqueueing jquery

Since the other wp_enqueue_script instances call out jquery as a dependency, there is no reason to enqueue it directly. Additionally, it breaks WordPress' wp_dequeue_script function when end users try to remove the edd-ajax script from pages that don't need it (jquery gets left enqueued when it may not be needed).
Merge pull request #2170 from mtekk/patch-1

Stop directly enqueueing jquery