EIP-3403 - Partial Removal of Refunds

[timbeiko]

Another gas refund proposal by @vbuterin: ethereum/EIPs#3403

Related to #255 #258 & #266

[holiman]

Related:https://gist.github.com/holiman/aa7d2d28a9747548a0a14321a1572b22

[timbeiko]

We agreed on ACD111 to not have this in London, but rather consider the to-be-created alternative, so closing this.