fix: remove usage of reserved per-action router fields

[javier-aliaga]

dapr/durabletask-protobuf#51 reserved the unused router fields on ScheduleTaskAction (4) and CreateChildWorkflowAction (5), which broke compilation since protos are downloaded from main at build time.

The runtime only reads the enclosing WorkflowAction.router, which was always set alongside the inner ones, so dropping the inner setters and their test assertions has no behavior change.

Description

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Issue reference

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Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.86%. Comparing base (5a6ccef) to head (940d48a).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1767   +/-   ##
=========================================
  Coverage     76.86%   76.86%           
  Complexity     2298     2298           
=========================================
  Files           243      243           
  Lines          7141     7141           
  Branches        745      745           
=========================================
  Hits           5489     5489           
  Misses         1287     1287           
  Partials        365      365           

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