[frogr] flatpak: Remove stable manifest and flatpakref files

[Mario Sanchez Prada <msanchez src gnome org>]

commit f45c6d52a8c70e830d327334643e1e8dcd5e91cb
Author: Mario Sanchez Prada <msanchez gnome org>
Date:   Tue Dec 26 14:41:37 2017 +0100

    flatpak: Remove stable manifest and flatpakref files
    
    The stable version of frogr is now built in flathub, so these ones
    are no longer needed. See https://github.com/flathub/org.gnome.frogr

 flatpak/org.gnome.frogr-stable.flatpakref |    8 -----
 flatpak/org.gnome.frogr-stable.json       |   44 -----------------------------
 2 files changed, 0 insertions(+), 52 deletions(-)