fsapp: remove pidbox replies on clean

[pmrowla]

When workers exit they will end up leaving filesystem broker control messages that never expire and will never be ack'd in the future, we should just purge them on clean

[codecov-commenter]

Codecov Report

Patch coverage: 52.63% and project coverage change: -5.95 ⚠️

Comparison is base (358a100) 79.12% compared to head (b547384) 73.18%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
- Coverage   79.12%   73.18%   -5.95%     
==========================================
  Files          21       21              
  Lines         987     1007      +20     
  Branches      154      154              
==========================================
- Hits          781      737      -44     
- Misses        179      235      +56     
- Partials       27       35       +8     

Impacted Files	Coverage Δ
src/dvc_task/app/filesystem.py	79.03% <28.57%> (-10.69%)	⬇️
src/dvc_task/worker/temporary.py	79.10% <81.25%> (-0.59%)	⬇️
tests/worker/test_temporary.py	93.93% <100.00%> (ø)

... and 6 files with indirect coverage changes

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