delete 2 parameters: registeredBy & registeredAt

[kappyhappy]

Issue #, if available:

Description of changes:
Fix workshop commands.
Current command causes the error shown as below.

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

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