Bug#991466: thunar needs gvfs-backends to read phone memory

[Akbarkhon Variskhanov <akbarkhon.variskhanov@gmail.com>]

Control: fixed -1 4.15.3-1

This was already addressed in Thunar 4.15.3-1, which added the
gvfs-backends package to its Suggests field. Considering that and also
the fact that both Debian Wiki[1] and the official Xfce
documentation[2] mention this, it's not within reason to add 30 or so
extra dependencies to Thunar. And it's extremely unlikely that the
gvfs-backends package will ever be marked as a direct dependency of
Thunar.

[1] https://wiki.debian.org/Thunar#FTP_.2F_SFTP_etc.
[2] https://docs.xfce.org/xfce/thunar/unix-filesystem#gnome_virtual_file_system