An envelope was voided due to the past due date to sign. One of the recipients signed the envelope and the other did not. I forgot to remove the one recipient. Is it possible to remove the Void message on the signed Agreement?

No, it is now a voided envelope. This is one of the main security features, that instills a Tamper Proof final PDF document. Basically the option is to send a new envelope. You can use the "Create a Copy" which makes resending the same envelope a little easier, basically it would copy the attachment, fields placed, Recipients, etc to make the process a little easier.