Remove hard error on session reuse

[rbren]

• This change is worth documenting at https://docs.all-hands.dev/
• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below
  nope

End-user friendly description of the problem this fixes or functionality that this introduces.

This was accidentally reintroduced in a recent PR

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Give a summary of what the PR does, explaining any non-trivial design decisions.

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Link of any specific issues this addresses.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:ba3d641-nikolaik   --name openhands-app-ba3d641   docker.all-hands.dev/all-hands-ai/openhands:ba3d641

[tofarr]

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