open editors css to hide twisite no longer needed

src/vs/workbench/parts/files/browser/media/explorerviewlet.css

@@ -174,11 +174,6 @@
 .explorer-viewlet:lang(ja) .explorer-open-editors .monaco-tree .monaco-tree-row .editor-group,
 .explorer-viewlet:lang(ko) .explorer-open-editors .monaco-tree .monaco-tree-row .editor-group { font-weight: normal; }
 
-/* Disable tree twistie */
-.explorer-viewlet .explorer-open-editors > .monaco-tree .monaco-tree-rows > .monaco-tree-row > .content:before {
-	display: none;
-}
-
 /* High Contrast Theming */
 .hc-black .monaco-workbench .explorer-viewlet .explorer-item,
 .hc-black .monaco-workbench .explorer-viewlet .open-editor,