refactor(robot-server): Delete obsolete workarounds for discriminated unions in Pydantic v1

[SyntaxColoring]

Overview

Now that we're on Pydantic v2, we can delete these old workarounds for pydantic/pydantic#3782. Closes EXEC-1065.

Test Plan and Hands on Testing

• Run a dev server, try sending a command to these endpoints, and make sure the errors reflect that the union discriminator is being used. In other words, Pydantic should only try parsing the input as the command you specified by commandType, not all possible commands. You'll know if this isn't working properly because the error message will be the length of the novel if you forget a param.

Review requests

None.

Risk assessment

Low if the manual test plan is done.