In the process of getting rid of docs/qmp-commands.txt, we managed
to regress on some of the text that changed after the point where
the move was first branched and when the move actually occurred.
For example, commit 3282eca4 for blockdev-snapshot re-added the
extra "options" layer which had been cleaned up in commit 0153d2f5.

This clears up all regressions identified over the range
02b351d8..bd6092e4:
https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg05127.html


as well as a cleanup to x-blockdev-remove-medium to prefer
'id' over 'device' (matching the cleanup for 'eject').

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>