Use Antrun plugin to eliminate javadoc version number in HTML

Use Antrun plugin to eliminate javadoc version number in HTML

This is the one issue that cannot be solved regarding reproducible
builds by setting javadoc options, because that header comment is
hard-coded into the JDK with no option to avoid it. I just created an
OpenJDK issue (internal review ID 9076583, not published yet) for it,
but that does not help us today.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>