stream_libarchive: disable tar support

Unfortunately, libarchive detects a stream of 0s as tar, as demonstrated
by "mpv /dev/zero". This is inconvenient in some cases.

One example is the .cue demuxer trying to open a raw audio .bin file,
which it allows only if probing fails (as .bin is raw and normally will
not look like any real file format). Although this use-case is
worthless.