Remove screenshot dimensions from appdata

Refer https://github.com/flathub/org.kde.falkon/pull/3#issuecomment-1064018275

Signed-off-by: Snehit Sah <snehitsah@protonmail.com>

linux/appdata/org.kde.falkon.appdata.xml

@@ -151,7 +151,7 @@
   </description>
   <screenshots>
     <screenshot type="default">
-      <image width="1105" height="855">https://cdn.kde.org/screenshots/falkon/falkon.png</image>
+      <image>https://cdn.kde.org/screenshots/falkon/falkon.png</image>
     </screenshot>
   </screenshots>
   <url type="homepage">https://falkon.org</url>