FreeBSD: Remove references to DEBUG_VFS_LOCKS

[markjdb]

Motivation and Context

FreeBSD used to have a separate debug option for VFS invariants checking, DEBUG_VFS_LOCKS. This was removed upstream since developers (including me) often forgot to enable it. Now these checks are enabled by the standard INVARIANTS option.

Description

ZFS had a couple of references to DEBUG_VFS_LOCKS. The change removes them without removing the correpsonding check.

How Has This Been Tested?

Built with --enable-invariants and --disable-invariants.

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)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• 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.

[Copilot]

Pull request overview

This PR removes references to the obsolete FreeBSD DEBUG_VFS_LOCKS option, which has been superseded by the standard INVARIANTS option. The change removes conditional compilation directives while preserving the actual assertion check functionality.

Changes:

• Removed the VNCHECKREF macro definition that was conditionally compiled with DEBUG_VFS_LOCKS
• Removed the conditional variable declaration vnode_t *dvp that was only used for the macro
• Removed the build system configuration for WITH_VFS_DEBUG in module/Makefile.bsd
• Replaced the macro invocation with a direct VNASSERT call

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
module/os/freebsd/zfs/zfs_vnops_os.c	Removed DEBUG_VFS_LOCKS macro definition and conditional variable, replaced macro usage with direct VNASSERT call
module/Makefile.bsd	Removed build configuration for WITH_VFS_DEBUG option

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