[React] Remove a bug work-around as it was fixed in the React Core

Revert #4548 and keep the tests.
Here is the fix at the React level facebook/react#7125.
@puranjayjain you might be interested in seeing this.

CHANGELOG.md

@@ -10,7 +10,6 @@ margin = (oldSize < 0.71) ?
   ((50 - 59.5 * oldSize) / 2) :
   (5.25 * oldSize);
 ```
-
 Examples:
 ```
 // Before:
@@ -21,6 +20,11 @@ Examples:
 <CircularProgress size={59.5} style={{margin: 5.25}} /> // Thickness is 3.5 by default
 <CircularProgress size={119} thickness={7} style={{margin: 10.5}} />
 ```
+(#4705)
+
+- Remove a workaround regarding the context propagation as it was fixed in the React Core.
+Upgrade to React v15.2.1 if you are affected. (#4729)
+
 
 ## 0.15.2
 ###### _Jul 7, 2016_

docs/src/app/components/pages/customization/Themes.js

@@ -227,7 +227,7 @@ class ThemesPage extends Component {
               actions={[
                 <FlatButton
                   label="Cancel"
-                  keyboardFocus={true}
+                  keyboardFocused={true}
                   onTouchTap={this.handleRequestCloseDialog}
                   primary={true}
                 />,

src/internal/RenderToLayer.js

@@ -1,8 +1,7 @@
-import React, {Component, PropTypes} from 'react';
+import {Component, PropTypes} from 'react';
 import {unstable_renderSubtreeIntoContainer, unmountComponentAtNode} from 'react-dom';
 
 import Dom from '../utils/dom';
-import MuiThemeProvider from '../styles/MuiThemeProvider';
 
 // heavily inspired by https://github.com/Khan/react-components/blob/master/js/layered-component-mixin.jsx
 class RenderToLayer extends Component {
@@ -110,15 +109,7 @@ class RenderToLayer extends Component {
         }
       }
 
-      /**
-       * We use the <MuiThemeProvider /> component as a work around for
-       * https://github.com/facebook/react/issues/6599.
-       */
-      const layerElement = (
-        <MuiThemeProvider muiTheme={this.context.muiTheme}>
-          {render()}
-        </MuiThemeProvider>
-      );
+      const layerElement = render();
       this.layerElement = unstable_renderSubtreeIntoContainer(this, layerElement, this.layer);
     } else {
       this.unrenderLayer();