Remove getTextContentAccessor (facebook#13434)

According to caniuse the only browsers that don't support textContent
are <=IE8, which we no longer support.

Author: aweary

packages/react-dom/src/client/ReactDOMSelection.js

@@ -6,7 +6,6 @@
  */
 
 import getNodeForCharacterOffset from './getNodeForCharacterOffset';
-import getTextContentAccessor from './getTextContentAccessor';
 import {TEXT_NODE} from '../shared/HTMLNodeType';
 
 /**
@@ -155,7 +154,7 @@ export function setOffsets(node, offsets) {
   const doc = node.ownerDocument || document;
   const win = doc ? doc.defaultView : window;
   const selection = win.getSelection();
-  const length = node[getTextContentAccessor()].length;
+  const length = node.textContent.length;
   let start = Math.min(offsets.start, length);
   let end = offsets.end === undefined ? start : Math.min(offsets.end, length);
 

packages/react-dom/src/client/getTextContentAccessor.js

@@ -5,8 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import getTextContentAccessor from '../client/getTextContentAccessor';
-
 /**
  * These variables store information about text content of a target node,
  * allowing comparison of content before and after a given event.
@@ -69,5 +67,5 @@ export function getText() {
   if ('value' in root) {
     return root.value;
   }
-  return root[getTextContentAccessor()];
+  return root.textContent;
 }