I have removed @streemian out of my posting key with only 1 command line in cli_wallet

update_account_auth_account magicstone1412 posting streemian 0 true

Your case should be,

update_account_auth_account ctyptouniverse posting minnowbooster 0 true

You can download cli_wallet at the end of my post. Hope it help!

If you don't feel confident with cli_wallet, please read this post (I do not test yet). But steemconnect will ask your password in that case. You can change your password after removing authorized minnowbooster account in case you don't believe in steemconnect