Remove version key in desktop.in

This is not for the Gajim version, its the version of the spec this
file conforms to.
This key is not required by the spec

data/org.gajim.Gajim.desktop.in

@@ -5,7 +5,6 @@ GenericName=Jabber IM Client
 Comment=A GTK+ Jabber client
 #Translators: Search terms to find this application. Do NOT translate or localize the semicolons! The list MUST also end with a semicolon!
 Keywords=chat;messaging;im;xmpp;bonjour;voip;
-Version=1.0.3
 Exec=gajim %u
 #Translators: Do NOT translate or transliterate this text (this is an icon file name)!
 Icon=org.gajim.Gajim