debian/patches: (sysctl_swap.patch) Use sysctl to get swap usage information for
GNU/kFreeBSD.

Remove debian/patches/fix-unused-result.patch, as the affected code was removed
by sysctl_swap.patch.
debian/lintian-overrides: Remove file; no longer needed.
debian/rules: Remove override_dh_fixperms target; no longer needed.
debian/control: Remove libkvm-dev Build-Depends; no longer needed.
debian/changelog: Update with recent changes.