remove StackName from CW event rule target id

[eliran89c]

remove AWS::StackName pseudo parameter from "sfRealTimeQueueMetricsCron.targets.1"

Description of changes:
when deploying this package as a nested stack it failed due to 64 characters limit

1 validation error detected: Value 'XXX-TTYSRYK8OZ3T-sfRealTimeQueue' at 'targets.1.member.id' failed to satisfy constraint: Member must have length less than or equal to 64 

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We can't merge this as customers could have multiple SF lambdas in their account so they need this disambiguator

[rafalwrzeszcz]

@srivanc This is absolutely not true, ID is only identifying target within same rule and this each alarm has separate targets.