Don't use mode argument (or check for _edd_payment_mode) anywhere in core

In the admin - most especially in the reporting area and in the payment history, we're getting some super slow queries due to joining the meta table for the payment mode.  This is unnecessary and should be avoided in core.

I'm going to take this opportunity to riff on Pippin's name a bit:

* If he wore Warby Parkers and skinny jeans - He'd be a Pipster.
* If he started a show on Fx - it would be called Pip/Tuck.
* If he started an online messaging service, naturally, it would be called PipChat.