qemu-img: implement short --help, remove global help() function

qemu-img: implement short --help, remove global help() function

now once all individual subcommands has --help support, remove
the large unreadable help() thing and replace it with small
global --help, which refers to individual command --help for
more info.

While at it, also line-wrap list of formats after 75 chars.

Since missing_argument() and unrecognized_option() are now unused,
remove them.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250531171609.197078-27-mjt@tls.msk.ru>
[kwolf: Fixed up style and formatting]
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>