Override RSS Header Background Image (#368)

After latest release RSS window header shows a tiling image caused by transparent background styling. I looked at other headers and for some reason this is the only one with this tiling image.

Before: https://i.imgur.com/Sk1Gs0a.png
After: https://i.imgur.com/AgSObmX.png

css/base/rutorrent/rutorrent-base.css

@@ -1800,3 +1800,7 @@ div#dlgEditRules div.dlg-header {
     background: var(--transparency-dark-10);
     color: var(--text);
 }
+
+div#dlgEditFilters div.dlg-header{
+    background-image:none;
+}