Remove old CSS that makes docs header stack on top of HaaS on mobile (#4681)

Co-authored-by: Paul Römer <paul@vaadin.com>

Author: veerapaananen

dspublisher/theme/global.css

@@ -118,13 +118,6 @@ dspublisher-header #haas-container {
   margin-bottom: 0;
 }
 
-/* Keep Haas elements below docs search */
-@media (max-width: 1024px) {
-  body:not(.haas-open) dspublisher-header {
-    position: relative;
-    z-index: 1;
-  }
-}
 
 [class*='docsHeader-'] {
   box-shadow: inset 0 -1px 0 0 var(--docs-divider-color-1), 0 -1px 0 0 var(--docs-divider-color-1);