Revert "Install and require OpenJDK 10."
Revert "Install and require OpenJDK 10."

This reverts commit 86b33fc0d95716454a5804b25a463a03ef8ca3ba.

vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa