flatpak: Remove --talk-name=org.gtk.vfs

The `--talk-name=org.gtk.vfs` statement should not be used in manifests
as there is no service with such name. The `--talk-name=org.gtk.vfs.*`
statement should be pretty enough for the GVfs access. See:
https://docs.flatpak.org/en/latest/sandbox-permissions.html#gvfs-access
Let's drop that statement.