MFC r348567: MFV r348555:
9690 metaslab of vdev with no space maps was flushed during removal

illumos/illumos-gate@4e75ba682600b2bf19d158577d528c3db65050e8

Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Serapheim Dimitropoulos <serapheim@delphix.com>