qemu-img: fix .hx and .texi disparity

qemu-img: fix .hx and .texi disparity

It turns out that having options listed in three places continues to be
a bad idea. I'm still toying with the idea of an improved infrastructure
here, but in the meantime, another bandaid.

There are three locations:
(1) .hx file, formatted as texi
(2) .hx file, formatted as human readable.
(3) .texi file, as section headers, formatted as texi.

You can compare the two summaries within the .hx file like so:

Human-readable command summaries:
`./qemu-img --help | grep 'Command syntax' -A14`
Detokenized texi command summaries:
`grep "@item" qemu-img-cmds.hx | sed -E 's|@var\{([^\}]*?)\}|\1|g'`

You can compare the two separate texi summaries like so:

Texi command summaries:
`grep "@item" qemu-img-cmds.hx"`
Texi command headers:
grep -E "@item.*@var" qemu-img.texi | tail -14

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20190409210655.777-1-jsnow@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>