Removing obsolete SVN tag for the WHIZARD beta release version of 3.0.0_beta
which is up to dependent files identical to the distribution tarball, and
identical to SVN revision r8433 from August 28, 2020. Note that there were
no SVN tags for releases 2.8.4 and 2.8.5 (and maybe upcoming 2.8.6) as they
are only in a separate GIT branch.