Remove several OP examples

Before examples can be migrated away from XStream to something else, we should trim them down.

I am proposing the following examples to be removed:

• batchscheduling has been introduced by a community member. It was merged without any test coverage (mea culpa), it doesn't have a constraint provider and not enough documentation for me to write one. It doesn't belong.
• cheaptime is a very complex use case which I designed 10 years ago to take second place in a competition; besides that, there was never any traction and the use case is niche.
• coachshuttlegathering is a synthetic use case which, so far, I have not seen anyone in the community mention. It is niche and does not showcase any unique feature.
• investment is a synthetic use case which I do not see any traction for. Furthermore the only two data sets we have are trivial.
• rocktour is TSP with a few extra trivial constraints. While we already have TSP and VRP, I do not see the value.

Some honorable mentions:

• tsp is trivial compared to VRP, and I question its usefulness. That said, travelling salesman is the poster boy of planning problems, so I am inclined to keep it just because of that. Also, it will be the last remaining example that is based on chaining, and not list variable.
• cloudbalancing and machinereassignment cover the same area of use cases. MR is much more complex and it has proven to be a good benchmark. CB is good as a getting-started use case, we have a lot of documentation around it, it is intuitively easy to understand and explain. Even though there technically is overlap, I'm inclined to keep them both as well.