TYPO3 Core

Since phpunit/phpunit version 7.4 the package contains an own randomizer option (order-by).

See https://github.com/fiunchinho/phpunit-randomizer, the ReadMe features a broken link even to phpunit 7.3, but it is not in the docs for this version.
I tested, and the last version working with `bin/phpunit-randomizer -c vendor/typo3/testing-framework/Resources/Core/Build/UnitTests.xml --order rand` would be phpunit 7.2.

With the latest test run, the randomizer call used by the nightly run even fails. The used phpunit version was 7.5 (released yesterday)

The day before, the nighly run used phpunit 7.1 as max version, no error was detected.

So here is my conclusion:
- quickfix would be to limit the max phpunit version to 7.2

- extend the test specs to detect which phpunit version is used, make the randomizer all until 7.2, above use phpunit with `order-by=random`.
- remove the fiunchinho/phpunit-randomizer package from the deps
- drop dependency phpunit <7.3.