Remove residual blank line at start of Makefile

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

zfs: merge openzfs/zfs@2e2a46e0a

Notable upstream pull request merges:
#15243 b53077a9e Add zfs_prepare_disk script for disk firmware install
#15298 2e2a46e0a Invoke zdb by guid to avoid import er

zfs: merge openzfs/zfs@2e2a46e0a

Notable upstream pull request merges:
#15243 b53077a9e Add zfs_prepare_disk script for disk firmware install
#15298 2e2a46e0a Invoke zdb by guid to avoid import errors
#15301 e5d70f467 ZIL: Avoid dbuf_read() in ztest_get_data()

Obtained from: OpenZFS
OpenZFS commit: 2e2a46e0a597b3ee606ea7dc5bc527459077322f

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