[BS5] remove ui theme selector - add darkmode toggler

data/web/admin.php

@@ -83,16 +83,12 @@ foreach ($RSPAMD_MAPS['regex'] as $rspamd_regex_desc => $rspamd_regex_map) {
   ];
 }
 
-$themes = array_diff(scandir('/web/css/themes'), array('..', '.'));
-$themes = array_filter((str_replace("-bootstrap.css", "", $themes)));
-
 $template = 'admin.twig';
 $template_data = [
   'tfa_data' => $tfa_data,
   'tfa_id' => @$_SESSION['tfa_id'],
   'fido2_cid' => @$_SESSION['fido2_cid'],
   'fido2_data' => $fido2_data,
-  'themes' => $themes,
   'gal' => @$_SESSION['gal'],
   'license_guid' => license('guid'),
   'api' => [