Revert "clean up img/decoding (#1411)"

This reverts commit c9675be.

includes/status.include

@@ -19,5 +19,4 @@ per [W3C Process - 6.4 Candidate Recommendation](https://www.w3.org/2017/Process
  <li><a href="https://github.com/w3c/html/pull/1329">The <code>:defined</code> pseudo-class</a>;</li>
  <li>Allowing multiple <{meta}> elements with <code>name="description"</code>;</li>
  <li>the <{rtc}> element;</li>
- <li>the <{img/decoding}> attribute for the <{img}> element.</li>
 </ul>

sections/attributes.include

@@ -225,12 +225,6 @@
         <a>valid duration string</a>
       </td>
     </tr>
-    <tr>
-      <th><{img/decoding}></th>
-      <td><{img}></td>
-      <td>A hint to request a/synchronous loading of images</td>
-      <td>"<code>sync</code>", "<code>async</code>", "<code>auto</code>"</td>
-    </tr>
     <tr>
       <th><code>default</code></th>
       <td><{track}></td>

sections/semantics-embedded-content.include

@@ -713,7 +713,6 @@
     (e.g., high-resolution displays, small monitors, etc) </dd>
     <dd><code>sizes</code> - Image sizes between breakpoints</dd>
     <dd><code>crossorigin</code> - How the element handles crossorigin requests</dd>
-    <dd><{img/decoding}> - Hint for requesting synchronous or asynchronous loading</dd>
     <dd><code>usemap</code> - Name of <a>image map</a> to use </dd>
     <dd><{img/ismap}> - Whether the image is a server-side image map</dd>
     <dd><code>width</code> - Horizontal dimension</dd>
@@ -753,7 +752,6 @@
           [CEReactions] attribute DOMString srcset;
           [CEReactions] attribute DOMString sizes;
           [CEReactions] attribute DOMString? crossOrigin;
-          [CEReactions] attribute DOMString decoding;
           [CEReactions] attribute DOMString useMap;
           attribute DOMString longDesc;
           [CEReactions] attribute boolean isMap;
@@ -764,6 +762,7 @@
           readonly attribute boolean complete;
           readonly attribute DOMString currentSrc;
           [CEReactions] attribute DOMString referrerPolicy;
+          [CEReactions] attribute DOMString decoding;
         };
       </pre>
     </dd>
@@ -899,13 +898,13 @@
   settings attribute</a>. Its purpose is to allow images from third-party sites that allow
   cross-origin access to be used with <{canvas}>.
 
-  The <dfn element-attr for="img"><code>decoding</code></dfn> attribute is an enumerated attribute.
-  It is an [=image decoding hint=] to request synchronous or asynchronous image loading.
-  Valid values are "<code>async</code>", "<code>async</code>", and "<code>auto</code>".
-  The [=missing value default=] and [=invalid value default=] are both "<code>auto</code>".
+  The <dfn element-attr for="img"><code>referrerpolicy</code></dfn> attribute is a <a>referrer policy attribute</a>. Its purpose is to
+  set the <a>referrer policy</a> used when <a>fetching</a> the image. [[!REFERRERPOLICY]]
 
-  The <dfn element-attr for="img"><code>referrerpolicy</code></dfn> attribute is a <a>referrer policy attribute</a>.
-  Its purpose is to set the <a>referrer policy</a> used when <a>fetching</a> the image. [[!REFERRERPOLICY]]
+  The <dfn element-attr for="img"><code>decoding</code></dfn> attribute indicates
+  the preferred method to <a for="image">decode</a> this image. The attribute,
+  if present, must be an [=image decoding hint=]. This attribute's
+  [=missing value default=] and [=invalid value default=] are both the {{auto}} state.
 
   <hr />