...
The file can be found in the following path: \\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\Machine.config
The row to be deleted is given below:
"<add name="ODP.NET, Unmanaged Driver" invariant="Oracle.DataAccess.Client" description="Oracle Data Provider for .NET, Unmanaged Driver" type="Oracle.DataAccess.Client.OracleClientFactory, Oracle.DataAccess, Version=4.121.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342" />
...