migration: Remove 'blk/-b' option from migrate commands

migration: Remove 'blk/-b' option from migrate commands

The block migration is considered obsolete and has been deprecated in
8.2. Remove the migrate command option that enables it. This only
affects the QMP and HMP commands, the feature can still be accessed by
setting the migration 'block' capability. The whole feature will be
removed in a future patch.

Deprecation commit 8846b5bfca ("migration: migrate 'blk' command
option is deprecated.").

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>