Get rid of java implementation

[sebastian-peter]

With ie3-institute/simona#1502, a new issue has been brought to the surface. The Java implementation uses an ancient library com.googlecode.matrix-toolkits-java:mtj. I tried replacing it with org.ojalgo:ojalgo, should be doable, but takes some more effort.

Taking more time to reflect on it, I think it makes more sense to get rid of the Java implementation entirely, for multiple reasons:

1. It's not used anymore
2. It takes effort to maintain it properly (which we don't afford currently)
3. It inflates simona because it brings unnecessary dependencies