feat(ptoken): <- remove all ERC777 hooks from that

[gskapka]

...per title.

NOTE: Hook calls have been commented out in the contract in question, though the hook logic remains.

NOTE: Test w/r/t the tokensReceivedHook have been skipped for now.

[allemanfredi]

LGTM!

btw i would add one test to test the upgrade just to be sure. You could:

• create a test contract called OldErc777 (or something like this) that still uses the real ERC777Upgradable implementation (import "@openzeppelin/contracts-upgradeable/token/ERC777/ERC777Upgradeable.sol")
• deploy the pToken contract using OldErc777
• do something just to write some value in the contract state
• upgrade the pToken contract using the the new implementation (import "./ERC777Upgradeable.sol")

[gskapka]

I've done one better because we need a more robust test for the upgrade compatibility since it's so critical.

So if you review the latest additions you'll see that new test.

Basically we use a child process to clone the whole repo to temp dir, checkout master there, flatten the pToken.sol contract, copy that contract into the main repo's ./contracts dir, then finally use ethers' upgrades.validateUpgrade fxn to check we've not broken the storage compatibility.

Having this test here (and runnable in the CI which I've also added) gives me much more confidence going forward since we're likely to be editing this contract more in future.

[allemanfredi]

LGTM!