[executor] return committed txns instead of txns to commit in 'commit_blocks'
[executor] return committed txns instead of txns to commit in 'commit_blocks'

Closes: #2958
Approved by: dmitri-perelman

aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra