We normally don't remove a runtime when the last app using it is
uninstalled, since runtimes are large and re-downloading it in the
future may be difficult. But if the runtime is end-of-life, there's a
reasonable chance it won't be used again, so uninstall it in that case.
Similarly, if the last app using a runtime is upgraded to a different
runtime, and the runtime is EOL, uninstall it.
A unit test is included, and the subsequent unit test also had to be
modified. Otherwise we get a "Update is older than current version"
error, since the runtime is installed from test-repo but
setup_repo_no_add() calls make_runtime() which uses the one in
runtime-repo instead, which is older than the one in test-repo.
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