Delete the line containing the SSH public key that you want to remove from the authorized_keys files associated with the opc user (/home/opc/.ssh/authorized_keys) and the oracle user (/home/oracle/.ssh/authorized_keys).
Caution:
The authorized_keys files may contain numerous keys and altering or removing the wrong key may result in a loss of functionality. To minimize the likelihood of an error make a copy of each authorized_keys file before making any modification. Also, rather than deleting the line containing the public key that you wish to remove, you can disable the key by tagging it with the @revoked marker. For example:
@revoked ssh-rsa AAAAB5W...
