Update createservice.md

[bluecrayon52]

The following command produces an error:

workshop:~/environment $ echo $TASK_DEF_NEW > /tmp/$TASK_DEF_FAMILY.json && 
> # Register ecs task definition #
> aws ecs register-task-definition \
>   --cli-input-json file:///tmp/$TASK_DEF_FAMILY.json

Parameter validation failed:
Unknown parameter in input: "registeredBy", must be one of: family, taskRoleArn, executionRoleArn, networkMode, containerDefinitions, volumes, placementConstraints, requiresCompatibilities, cpu, memory, tags, pidMode, ipcMode, proxyConfiguration, inferenceAccelerators
Unknown parameter in input: "registeredAt", must be one of: family, taskRoleArn, executionRoleArn, networkMode, containerDefinitions, volumes, placementConstraints, requiresCompatibilities, cpu, memory, tags, pidMode, ipcMode, proxyConfiguration, inferenceAccelerators 

Description of changes: Removing unknown parameters registeredAt and registeredBy from new task definition for ecs register-task-definition request.

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[bluecrayon52]

duplicate request (see #112)