How to: Remove the Witness from a Database Mirroring Session (SQL Server Management Studio)
You can remove the witness from a session if you are connected to the current principal server.
To remove the witness
Connect to the principal server instance and, in the Object Explorer pane, click the server name to expand the server tree.
Expand Databases, and select the database whose witness you want to remove.
Right-click the database, select Tasks, and then click Mirror. This opens the Mirroring page of the Database Properties dialog box.
To remove the witness, delete its server network address from the Witness field.
Note If you switch from high-safety mode with automatic failover to high-performance mode, the Witness field is automatically cleared.