RootCanal: Clean up device and phy allocations

Bug: 159847796
Bug: 154020729
Test: cert/run --host
  manual test:
      out/host/linux-x86/bin/root-canal & sleep 1 && \
          python3 scripts/test_channel.py 6401 < scripts/start_and_stop
Change-Id: I1a8722f83920e298cfaec4f54d44d85c212c7cc8