Revert "Fix raw sends on encrypted datasets when copying back snapshots"

Commit d1d4769 takes into account the encryption key version to
decide if the local_mac could be zeroed out. However, this could lead
to failure mounting encrypted datasets created with intermediate
versions of ZFS encryption available in master between major releases.
In order to prevent this situation revert d1d4769 pending a more
comprehensive fix which addresses the mount failure case.

Reviewed-by: George Amanakis <gamanakis@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #11294
Issue #12025
Issue #12300
Closes #12033