Remove Deferred/Scheduled transactions

[heifner]

Deferred transactions were announced as deprecated in v2.0.0-rc1 on 2019/10/07. Seeking feedback on adding a protocol feature to disable them.

• Work was started Add deprecate_deferred_transactions protocol feature EOSIO/eos#8697
• Not sure what system contract work is still needed. A number of PRs removing use of deferred transactions have already been merged. e.g. [develop-deprecate-deferred-trx] Deprecate Deferred Transactions EOSIO/eosio.contracts#447 & Use authorization of bidder for bidrefund deferred transaction - v1.7.x EOSIO/eosio.contracts#381 - Use authorization of bidder for bidrefund deferred transaction - develop EOSIO/eosio.contracts#384

[DenisCarriere]

👍 deprecating deferred transactions, there are currently no production smart contracts that depend on deferred transactions on EOS Mainnet since this feature was incredibly unreliable and transactions were expiring before it can be propagated to the network.

As for PRs merged, most system level smart contracts on EOS have been resolved with the exception of eosio::undelegatebw & eosio.wrap::exec.

• Name bidding
• MSIG exec
• Unstaking resources
• Wrap exec