Remove Java version limit for classic Java runners

It seems there's an artificial restriction in https://github.com/apache/beam/blob/master/runners/core-construction-java/src/main/java/org/apache/beam/runners/core/construction/Environments.java#L119 that's preventing Beam from running natively on Java > 11. This restriction should only apply when trying to use the portable runner, but it's enforced everywhere due to a constant failing to initialize there.