Normative: Remove timezone and currency

From discussion at tc39/ecma402#105 ,
it seems that we don't have agreement to add these extension keys
to locales. We can keep considering that option for the future, but
for now, removing them from Intl.Locale.

spec.html

@@ -28,10 +28,6 @@ <h1>Abstract Operations for Locale Objects</h1>
           <td>collation</td>
           <td>co</td>
         </tr>
-        <tr>
-          <td>currency</td>
-          <td>cu</td>
-        </tr>
         <tr>
           <td>hourCycle</td>
           <td>hc</td>
@@ -48,10 +44,6 @@ <h1>Abstract Operations for Locale Objects</h1>
           <td>numberingSystem</td>
           <td>nu</td>
         </tr>
-        <tr>
-          <td>timeZone</td>
-          <td>tz</td>
-        </tr>
       </table>
     </emu-table>