Remove DES from SecureStore

[akwick]

During an empirical study to understand the nature of cryptographic misuses in enterprise-driven projects on GitHub, we randomly inspected a few of the misuses. One of the misuses for which we could confirm as a true positive of the analysis, CogniCryptSAST, is in this project.

• com.openkm.util.SecureStore: Use DES as encryption. However, DES is not considered as secure anymore. Industrial tools like SonarSource consider the usage of DES as critical as well.

[darkman97i]

Thanks for the advisor. Really was an old section of code not used, I will remove it.