Linux file pickers are not here anymore

Change-Id: I0748afe45c2ff42c840e792df9ceba980dcdbed6
Reviewed-on: https://gerrit.libreoffice.org/7289Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

fpicker/README

-Native file pickers for Unix and Windows (file open dialog) GTK+, KDE, Windows.
+Native file pickers for OS X and Windows (file open dialog).