Remove our fork of substrate-validator-set pallet

[sameh-farouk]

Check if we can now remove our fork of substrate-validator-set pallet

[DylanVerstraete]

https://github.com/gautamdhameja/substrate-validator-set/tree/master is on polkadot-0.9.43, tfchain is on polkadot-0.9.42 so we can upgrade if we use latest polkadot but #802 is more important imo

[renauter]

I see https://github.com/gautamdhameja/substrate-validator-set/ is now on polkadot 1.1.0 and we want to be upgrade to 1.4.0
I also see an extrinsic we have - add_validator_again() - and it is not present on https://github.com/gautamdhameja/substrate-validator-set/
So not sure if removing the fork is the best