chore: drop dead code and the stale wireguard-tools dependency [P2]

wireguard-tools was still declared in Depends and in the runtime package list installed by
tools/build.sh --prepare-runtime-env. Since peer discovery moved to docker exec, no code
path invokes a host-side wg, and check_host_tools stopped requiring it. The declaration
was therefore installing a package the harness never calls and misrepresenting the actual
architecture to anyone reading the control file. Removed from both places.

Three items were carrying #[allow(dead_code)], which is a way of silencing the compiler
about a real question rather than answering it:

- SysctlTuningStatus.desired duplicated data that is already in .current - every
  SysctlValue holds both the desired and the current value, so the second Vec was the same
  information cloned on every inspect call and read by nobody;
- SysctlValue.managed was always set to true and never read. Ownership is decided per file
  by the marker, not per key, so the field encoded nothing;
- unix_now() in the reboot scheduler, along with the SystemTime and UNIX_EPOCH imports it
  needed. The module works in chrono NaiveDateTime throughout.

All three are removed rather than annotated. The workspace now builds clean under
-D warnings with no dead_code exceptions anywhere.

cargo test --workspace: 158 + 4 passed. clippy -D warnings clean.

tools/build.sh

@@ -37,7 +37,6 @@ BUILD_PACKAGES=(
 
 RUNTIME_PACKAGES=(
   iproute2
-  wireguard-tools
   nftables
   kmod
   util-linux
@@ -355,7 +354,7 @@ Section: net
 Priority: optional
 Architecture: amd64
 Maintainer: AWG2 Harness
-Depends: libc6, iproute2, wireguard-tools, nftables, kmod, util-linux, procps, systemd
+Depends: libc6, iproute2, nftables, kmod, util-linux, procps, systemd
 Description: Host-side orchestrator for AmneziaWG traffic shaping and lifecycle recovery
  AWG2 Harness manages AmneziaWG traffic shaping, IFB ingress shaping,
  nftables anti-torrent guard, reboot scheduling, swap setup and daemonized