MFV 313786

MFV 313786

7500 Simplify dbuf_free_range by removing dn_unlisted_l0_blkid

illumos/illumos-gate@653af1b809998570c7e89fe7a0d3f90992bf0216
https://github.com/illumos/illumos-gate/commit/653af1b809998570c7e89fe7a0d3f90992bf0216

https://www.illumos.org/issues/7500
  With the integration of:

    commit 0f6d88aded0d165f5954688a9b13bac76c38da84
    Author: Alex Reece <alex@delphix.com>
    Date:   Sat Jul 26 13:40:04 2014 -0800
    4873 zvol unmap calls can take a very long time for larger datasets

  the dnode's dn_bufs field was changed from a list to a tree. As a result,
  the dn_unlisted_l0_blkid field is no longer necessary.

Author: Stephen Blinick <stephen.blinick@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>