Undo a single deprecation change

Author: joebingham-wk

lib/react.dart

@@ -2833,9 +2833,9 @@ _createDOMComponents(creator) {
 /// > __DEPRECATED.__
 /// >
 /// > Environment configuration is now done by default and should not be altered. This can now be removed.
-/// > This will be removed in 7.0.0, along with other configuration setting functions.
+/// > This will be removed in 6.0.0, along with other configuration setting functions.
 @Deprecated(
-    'Environment configuration is now done by default. You can remove this. Will be removed from this library in the 7.0.0 release.')
+    'Environment configuration is now done by default. You can remove this. Will be removed from this library in the 6.0.0 release.')
 void setReactConfiguration(
   domCreator,
   customRegisterComponent, {