Examples tests: test_equality should request no duplicate reference

To add

test_equality(scatter2d/CoreShellNanoparticles2 scatter2d/CoreShellNanoparticles 2e-10)

to Tests/Examples/CMakeLists.txt, we had to also commit Tests/ReferenceData/ExamplesMini/scatter2d/CoreShellNanoparticles2.int.gz, which duplicates Tests/ReferenceData/ExamplesMini/scatter2d/CoreShellNanoparticles.int.gz.

When implemented correctly, test_equality should take the reference data from the alternate simulation we want to compare with.

added CMake cleanup test labels

assigned to @j.wuttke

mentioned in commit 82e2368a

mentioned in merge request !1703 (merged)

closed with commit a6838a6e

mentioned in commit a6838a6e