Use the new g_drive_is_removable over g_drive_is_media_removable

g_drive_is_removable seems to be more reliable for detecting removable USB HDD partitions

glib min version bumped to 2.50.0 (and gio, etc.), the minimum version which provides g_drive_is_removable

Same bug for thunar: xfce/thunar#384 (closed)