[gnome-apps-nightly] Remove migrated apps

[Mathieu Bridon <mbridon src gnome org>]

commit f01ab9407dc4aff3ef64a0188bc74b34935b2b23
Author: Jordan Petridis <jpetridis gnome org>
Date:   Mon Sep 30 14:23:55 2019 +0300

    Remove migrated apps
    
    We now build nightlies directly from the Gitlab CI, and they are pushed
    to a new repository:
    
    https://mail.gnome.org/archives/desktop-devel-list/2019-September/msg00028.html
    
    Not all apps were migrated though so we haven't decommissioned this
    repository yet.
    
    This commit removes those apps which have already been migrated to the
    new way of doing things, so that we don't continue building them here
    for nothing.

 NautilusDevel.flatpakref  | 8 --------
 gnome-calendar.flatpakref | 8 --------
 org.gnome.Calendar.app    | 3 ---
 3 files changed, 19 deletions(-)