Remove unused method.

The last usage was removed in 91e749c.

Author: bgrainger

src/MySqlConnector/MySqlClient/MySqlCommand.cs

@@ -172,13 +172,6 @@ private void VerifyNotDisposed()
 				throw new ObjectDisposedException(GetType().Name);
 		}
 
-		private void VerifyValid()
-		{
-			Exception exception;
-			if (!IsValid(out exception))
-				throw exception;
-		}
-
 		private bool IsValid(out Exception exception)
 		{
 			exception = null;