DOC: remove appveyor badge from readme (#22829)

Author: jreback

README.md

@@ -53,14 +53,6 @@
     </a>
   </td>
 </tr>
-<tr>
-  <td></td>
-  <td>
-    <a href="https://ci.appveyor.com/project/pandas-dev/pandas">
-    <img src="https://ci.appveyor.com/api/projects/status/86vn83mxgnl4xf1s/branch/master?svg=true" alt="appveyor build status" />
-    </a>
-  </td>
-</tr>
 <tr>
   <td></td>
   <td>