Delete dead code: dbuf_loan_arcbuf

[asomers]

It's been dead ever since 5fa356e

Sponsored by: ConnectWise
Signed-off-by: Alan Somers asomers@gmail.com

Motivation and Context

General code maintenance

Description

Delete an unused function definition

How Has This Been Tested?

Haven't tested it at all. Relying on CI.

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.

[amotin]

Not that I have objections, but after this arc_loan_inuse_buf() becomes unused, etc. I'd say would be good to investigate which of this code is still alive and could be possibly reused one day, and which may be long broken.