MFV r337175: 9487 Free objects when receiving full stream as clone

All objects after the last written or freed object are not supposed to
exist after receiving the stream. We should free them accordingly, as if
a freeobjects record for them had been included in the stream.

zfsonlinux/zfs@48fbb9ddbf2281911560dfbc2821aa8b74127315
illumos/illumos-gate@7864b8192b8d30471fa2240466d516292e5765b8

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>
Author: Paul Dagnelie <pcd@delphix.com>