unreproducible MAVEN_BUILD_TIMESTAMP

[bmwiedemann]

While working on reproducible builds for openSUSE, I found that
our javaparser 3.24.2 package varied from an embeded MAVEN_BUILD_TIMESTAMP value - probably
from https://github.com/javaparser/javaparser/blob/48dfd6d/javaparser-core/src/main/java-templates/com/github/javaparser/JavaParserBuild.java#L12
from https://github.com/javaparser/javaparser/blob/48dfd6d/javaparser-core/pom.xml#L29

There should be some way to create 2 bit-identical builds.

[jlerbsc]

I have no idea why this timestamp was added. Certainly to differentiate artifacts. It is better to base your comparison between the builds on other criteria.