Remove selfdestructs

[spalladino]

Until we support initialization of logic contracts in zOS, self-destructable contracts are open to being accidentally killed (see https://github.com/OpenZeppelin/openzeppelin-zos/blob/master/contracts/drafts/BreakInvariantBounty.sol#L68 for an example).

We should remove all selfdestruct calls from the oz-zos codebase.

Thanks @cwhinfrey for the report!

[cwhinfrey]

Sure thing! 👍

[nventuro]

What do you propose we do in this scenario? selfdestruct sorf ot makes sense there (though it could be argued it also makes sense in the claim scenario), and I'd prefer not to introduce further differences between oz and oz-zos. I'd leave it out of this release altogether, and wait until that is fixed upstream (OpenZeppelin/openzeppelin-contracts#1384).

[spalladino]

@nventuro I'd either remove the contract altogether as you mention, or change the selfdestruct to a owner().transfer(this.balance), since the behaviour we want is to transfer all funds to the owner.

[nventuro]

This has now been fixed in openzeppelin-solidity (OpenZeppelin/openzeppelin-contracts#1385), and will go into 2.0-rc4. I'll keep it out of this oz-zos release, and add it back once we merge rc4 here.

[nventuro]

Closed via #28