fix(docs): unnecessary log group in Step Functions state machine x-ra…

…y example (aws#16159)

Removes an unnecessary log group definition from the code example for enabling X-Ray in the State Machine.

fixes aws#16158

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packages/@aws-cdk/aws-stepfunctions/README.md

@@ -593,8 +593,6 @@ new sfn.StateMachine(stack, 'MyStateMachine', {
 Enable X-Ray tracing for StateMachine:
 
 ```ts
-const logGroup = new logs.LogGroup(stack, 'MyLogGroup');
-
 new sfn.StateMachine(stack, 'MyStateMachine', {
     definition: sfn.Chain.start(new sfn.Pass(stack, 'Pass')),
     tracingEnabled: true