gnome-themes-extra: correct the recipe name
Per https://gitlab.gnome.org/GNOME/gnome-themes-extra/-/blob/master/README.md,
gnome-themes-extra ever named as gnome-themes-standard.
So rename the recipe name to reflect the
current status to avoid confusion.
Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>