update ruoyi-ui/src/assets/styles/element-ui.scss.

@@ -82,3 +82,11 @@
 .el-range-separator {
   box-sizing: content-box;
 }
+
+.el-menu--collapse
+  > div
+  > .el-submenu
+  > .el-submenu__title
+  .el-submenu__icon-arrow {
+  display: none;
+}
\ No newline at end of file