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

[behlendorf]

Motivation and Context

Issue #11294, #12025, #12300

Description

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.

@gamanakis please review.

How Has This Been Tested?

This is a clean revert which was verified to resolve the mount failures
in the referenced issues.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.