floss: hcidoc: Remove dependency to tokio

hcidoc doesn't use tokio. The tokio dependency would cause tokio uprev
issue in chromeos/src/third_party/rust_crates/.

Bug: 262928525
Tag: #floss
Test: ./build.py --target utils
Change-Id: I1bd99cfbe7f17006b1e1a857f3470ddbe63c6dae