Remove usage of UnitTestCase

plugins/ExamplePlugin/tests/Unit/SimpleTest.php

plugins/VisitTime/tests/Unit/AddSegmentByLabelInUTCTest.php

tests/PHPUnit/Framework/TestCase/UnitTestCase.php

tests/PHPUnit/Integration/AssetManagerTest.php

tests/PHPUnit/Integration/CacheTest.php

...Unit/Integration/Plugin/Dimension/ActionDimensionTest.php

.../Integration/Plugin/Dimension/ConversionDimensionTest.php

...ration/Plugin/Dimension/DimensionMetadataProviderTest.php

...PUnit/Integration/Plugin/Dimension/VisitDimensionTest.php

tests/PHPUnit/Unit/Archive/ChunkTest.php

tests/PHPUnit/Unit/CacheTest.php

tests/PHPUnit/Unit/FilesystemTest.php