Remove support-8.4.x

Author: charsbar

bin/test_workflows.pl

@@ -8,7 +8,7 @@
 my %tags  = map { $_ => 1 } @{ $local->{jobs}{'pull-and-push'}{strategy}{matrix}{tag} // [] };
 $tags{centos6} = 1;    # special case
 
-my @branches = qw(develop support-8.8.x support-8.4.x support-8.0.x);
+my @branches = qw(develop support-8.8.x support-8.0.x);
 my @repos    = qw(movabletype movabletype-addons movabletype-plugins);
 
 my %used;