docs: Removed READ_EXTERNAL_STORAGE from 'normal' permissions

Per communication from Ben, READ_EXTERNAL_STORAGE was incorrectly
marked as a 'normal' permission in preview 1, and is properly
changed to 'dangerous' for preview 2. Updating the docs accordingly.

See first comment for doc stage location.

Change-Id: I0f824fb9689d2e7323e505b0200fda23eaa71eed
diff --git a/docs/html/preview/features/runtime-permissions.jd b/docs/html/preview/features/runtime-permissions.jd
index 79f0d88..95b4120 100644
--- a/docs/html/preview/features/runtime-permissions.jd
+++ b/docs/html/preview/features/runtime-permissions.jd
@@ -952,10 +952,6 @@
   </li>
 
   <li>
-    <code>android.permission.READ_EXTERNAL_STORAGE</code>
-  </li>
-
-  <li>
     <code>android.permission.REORDER_TASKS</code>
   </li>