Don't set legacy version for Mullvad Browser

We seem to have a similar problem in update_responses when signing Mullvad Browser 14.0a8 as was fixed in f61208a8. I attempted to patch up the file with the following diff:

diff --git a/tools/update-responses/update_responses b/tools/update-responses/update_responses
index d7d2517c..f7294299 100755
--- a/tools/update-responses/update_responses
+++ b/tools/update-responses/update_responses
@@ -351,6 +351,7 @@ sub get_response {
     $writer->xmlDecl;
     $writer->startTag('updates');
     foreach my $version (@$versions) {
+        next unless $config->{versions}{$version}{incremental_from};
         if (get_config($config, $version, $os, 'unsupported')) {
             $writer->startTag('update',
                 unsupported => 'true',
@@ -397,6 +398,7 @@ sub write_responses {
     my $versions = as_array($config->{channels}{$channel});
     my (%oses, %langs, %from_versions);
     foreach my $version (@$versions) {
+        next unless $config->{versions}{$version}{incremental_from};
         get_version_files($config, $version);
         get_buildinfos($config, $version);
         my $files = $config->{versions}{$version}{files};
@@ -444,6 +446,7 @@ sub write_htaccess {
     my (%oses, %langs, %from_versions);
     my $migrate_langs;
     foreach my $version (@$versions) {
+        next unless $config->{versions}{$version}{incremental_from};
         $migrate_langs = $config->{versions}{$version}{migrate_langs}
                                 if $config->{versions}{$version}{migrate_langs};
         my $files = $config->{versions}{$version}{files};

But I'm not convinced it worked correctly given the generation of xmls with 13.5a11 in the name.

In the meantime, I've rolled back the commit and will remove the builds pushed to staticiforme.torproject.org

@boklm can you take a look at this and re-sign Mullvad Browser 14.0a8?