tdeioslave/sftp: use free to destroy mCallbacks

As it allocated via malloc() rather than new.

Signed-off-by: Alexander Golubev <fatzer2@gmail.com>
(cherry picked from commit 688544193f)

tdeioslave/sftp/tdeio_sftp.cpp

@@ -599,7 +599,7 @@ sftpProtocol::~sftpProtocol() {
 #endif
   closeConnection();
 
-  delete mCallbacks;
+  free(mCallbacks);
 
   /* cleanup and shut down cryto stuff */
   ssh_finalize();