Do not specify an exact size for the appdata screenshot

This is unnecessary and breaks as soon as we want to update the
screenshots.

src/org.kde.kgeography.appdata.xml

@@ -314,7 +314,7 @@
       <caption xml:lang="uk">Вивчення географічних назв за допомогою KGeography</caption>
       <caption xml:lang="x-test">xxTraining geography with KGeographyxx</caption>
       <caption xml:lang="zh-CN">使用 KGeography 训练地理知识</caption>
-      <image type="source" width="1030" height="617">https://cdn.kde.org/screenshots/kgeography/kgeography.png</image>
+      <image type="source">https://cdn.kde.org/screenshots/kgeography/kgeography.png</image>
     </screenshot>
   </screenshots>
   <project_group>KDE</project_group>