AppData: Avoid repeating app name at beginning of description

[cassidyjames]

Something I noticed when Reminduck was featured on the AppCenter homepage:

https://github.com/matfantinel/reminduck/blob/b66efd6657ed74da38be5ba94a8e3ef51f651989/data/com.github.matfantinel.reminduck.appdata.xml.in#L10

It's not really needed since the app name is right above. :)