* Delete core-java-lang-oop module (remaining code
was duplicate of core-java-lang-syntax where it really belonged)
* Moved code from https://www.baeldung.com/java-eclipse-equals-and-hashcode to core-java-lang where it belong
* Delete core-java-lang-oop-2 module
* Delete core-java-lang-oop-3 module
* Delete core-java-lang-oop-4 module