databases/mysql-connector-java51: unpin openjdk8 and deprecate

The build only needed to be less strict in javadoc to compile with modern JDK.

Deprecation:

• superseded by databases/mysql-connector-j
• mysql 5.1 is not in the ports tree anymore
• no users of this port in the tree anymore
• this is the only port keeping deprecated log4j in the ports tree
• this port only copies a jar. There are better ways to get a plain jar in your Java project.
• the original reason for this port was "to provide continued support for Java 1,6 and 1.7 users". Java 6 and 7 are removed from the ports tree in 2016 and 2023.

NB: removed the run depends on java. It is just a library. The final application
will decide the Java version it runs on. No need to install an extra JDK.

PR: 294389
Approved-by: maintainer timeout (ultima@)