Dropdown: fix style (ElemeFE#14907)

Author: doing123

packages/theme-chalk/src/dropdown.scss

@@ -69,8 +69,6 @@
   border: 1px solid $--border-color-lighter;
   border-radius: $--border-radius-base;
   box-shadow: $--dropdown-menu-box-shadow;
-  max-height: 400px;
-  overflow: auto;
 
   @include e(item) {
     list-style: none;