refactor(components): remove redundant code in some components

src/components/Dropdown/DropdownMenu.js

@@ -1,4 +1,4 @@
-import { PropTypes } from 'prop-types'
+import PropTypes from 'prop-types'
 
 const DropdownMenu = () => null
 

src/components/Form/index.js

@@ -12,7 +12,5 @@ export {
   FormInput,
   FormSelect,
   Option,
-  FormTextarea,
-  Form as Form2,
-  FormItem as FormItem2
+  FormTextarea
 }

src/components/Nav/NavItem.js

@@ -1,7 +1,7 @@
 import React, { Component } from 'react'
 import PropTypes from 'prop-types'
 import { Link } from 'react-router'
-import classnames from 'classnames'
+import cx from 'classnames'
 import Icon from '../Icon'
 
 class NavItem extends Component {
@@ -75,7 +75,7 @@ class NavItem extends Component {
       Item = <Link to={href}>{NavIcon}{title}{Toggle}</Link>
     }
 
-    const classNames = classnames(
+    const classNames = cx(
       'cmui-nav__item',
       {
         'cmui-nav__item--open': open,

src/components/Select/index.js

@@ -1,4 +1,4 @@
 import Select from './Select'
 import Option from './Option'
 
-export { Select, Option, Select as Select2, Option as Option2 }
+export { Select, Option }