test(webapp): drop the cancelTaskAttemptDependencies container test

Importing the service pulls the cancel chain, which eagerly initializes the
concurrency tracker singleton and requires REDIS_HOST/REDIS_PORT at import
time, so the suite cannot load in the unit-test shards without stacking
mocks. The decompose it covered is exercised by the analogous batch-results
container test and confirmed by review, so drop this one rather than mock
the tracker and cancel chain.

Author: d-cs