Remove Control.Custom and update docs with correct approach for custom components

Author: andrewhl

docs/guides/react-native.md

@@ -111,37 +111,23 @@ export default Form;
 ```
 
 ## Using Custom Form Components
-If you are using a third-party form control component that delegates to a standard React Native iOS form control, you can use `Control.Custom` and provide a `delegate` prop. The `component` prop in this case is the custom component you're using.
-
-The supported controls are:
-
-* 'MapView'
-* 'Picker'
-* 'Switch'
-* 'TextInput'
-* 'DatePickerIOS'
-* 'SegmentedControlIOS'
-* 'Slider'
-
-Any custom form control can be used so long as it ultimately resolves to one of these React Native controls.
+To use a third-party form control component select the appropriate `Control` type (e.g., `Control.TextInput`) and override the `component` prop with your custom component. The custom component must resolve to one of the supported React Native form control types. See the supported types [here](#native-controls). 
 
 ```jsx
 import React from 'react-native';
 import { Form, Control } from 'react-redux-form/native';
-import { Input, Item } from 'native-base';
+import { Input } from 'native-base';
 
 class Form extends React.Component {
   render() {
     return (
-      <Form model="user"> 
-        <Item regular>
-          <Control.Custom
-            placeholder="Last Name"
-            model=".last_name"
-            component={Input}
-            delegate="TextInput"
-          />
-        </Item>
+      <Form model="user">
+        <Control.TextInput
+          placeholder="Last Name"
+          model=".last_name"
+          component={Input}
+          delegate="TextInput"
+        />
       </Form>
     );
   }

src/native.js

@@ -149,34 +149,6 @@ Control.Slider = (props) => (
   />
 );
 
-Control.Custom = (props) => {
-  const delegates = [
-    'MapView',
-    'Picker',
-    'Switch',
-    'TextInput',
-    'DatePickerIOS',
-    'SegmentedControlIOS',
-    'Slider',
-  ];
-
-  if (! props.delegate || ! delegates.includes(props.delegate)) {
-    throw new Error(`Delegate not found. Must be one of: [${delegates.map(d => `'${d}'`)}]`);
-  }
-  const CustomComponent = Control[props.delegate];
-
-  return (
-    <CustomComponent
-      component={props.component}
-      {...omit(props, 'mapProps')}
-    />
-  );
-};
-
-Control.Custom.propTypes = {
-  delegate: PropTypes.string.isRequired,
-};
-
 const NativeForm = (props) => <Form component={View} {...omit(props, 'mapProps')} />;
 const NativeFieldset = (props) => <Fieldset component={View} {...omit(props, 'mapProps')} />;
 const NativeErrors = (props) => (