Remove unused className prop (#7800)

This prop is not checked by the component it's passed into, and that
class doesn't correspond to any style rules.

ui/app/components/app/menu-bar/menu-bar.component.js

@@ -68,7 +68,6 @@ export default class MenuBar extends PureComponent {
         {
           accountDetailsMenuOpen && (
             <AccountDetailsDropdown
-              className="menu-bar__account-details-dropdown"
               onClose={() => this.setState({ accountDetailsMenuOpen: false })}
             />
           )