chore: Drop viz_hugr test utils

[aborgna-q]

See CQCL/hugr#1789

webbrowser now requires rust 1.81 on linux targets, so we better just drop it.

Also removes a couple unused dependencies detected with cargo-machete

[ss2165]

thanks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.62%. Comparing base (51a1424) to head (3099eeb).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #734      +/-   ##
==========================================
- Coverage   82.67%   82.62%   -0.06%     
==========================================
  Files          62       62              
  Lines        7234     7234              
  Branches     6978     6978              
==========================================
- Hits         5981     5977       -4     
- Misses        880      883       +3     
- Partials      373      374       +1     

Flag	Coverage Δ
python	82.42% <ø> (ø)
rust	82.63% <ø> (-0.06%)	⬇️

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