Double-edge Venom card: remove Sting, add low-power brief -rPois

With all the other changes meant to provide even bottom-power cards with a
flashy, obvious effect, the straight conjurations card stand out for mostly
being plain and weak. One of the more obvious points is the Venom card,
which was just sting | venom bolt | poison arrow. Straightforwardly weak,
since rPois isn't rare and sting is next to harmless.

The first two card power tiers are venom bolt | venom bolt or poison arrow,
but at those same tiers, you will get 10-15 | 5-10 turns of rPois-. This
is meant to have some of the trade-offs like other cards (twisters, hostile
summons) with only situational and pre-aware lethality (compare to the
excess that is drawing legendary pain cards and getting tormented).
You might want to excercise some caution in using that destruction deck
against swamp dragons or Snake, but the chance of a poison arrow should be
a good exchange.

Also, purge all these tabs left in decks.cc, ugh.