[dpoll] Platform beneficiaries are reduced to 5%

With the commit 1508f09b, dPoll platform beneficiaries are reduced to 5%. (instead of 10%).

This decision is made to support authors more with the upcoming 50%/50% author/curation reward split decided with HF21.

5% of the beneficiary rewards go to delegators. We're considering removing the beneficiaries entirely, but we also want to share something with our delegators, so it's a dead-end, at the moment. Shoot in the comments if you have any ideas.