[proposal] drop Junit4 runtime

This came up as part of

- https://github.com/eclipse-pde/eclipse.pde/pull/2071

and I noticed that we have a dedicated junit4 runtime. Given the JUnitVintage engine can execute JUnit4/3 test I wonder what is the added value of the JUnit4 runtime here?

So if we do not have one, maybe its time to delete?

FYI @akurtakov @iloveeclipse

The proposal points to a dedicated JUnit 4 runtime and links eclipse.pde pull request #2071; start by examining that context and locating the runtime in this repository. Determine whether JUnit Vintage makes it redundant, then identify what deletion would affect; done means the project no longer needs the dedicated runtime without breaking test execution. The issue has had no recent discussion, so seek maintainer guidance before starting.

Written by the indexing model from the issue text.