test/aws_lambda_function: Fix failing tests related to 'runtime'

[radeksimko]

This is to address the following test failure:

=== RUN   TestAccAWSLambdaFunction_runtimeValidation_noRuntime
--- FAIL: TestAccAWSLambdaFunction_runtimeValidation_noRuntime (64.36s)
    testing.go:494: Step 0, no error received, but expected a match to:
        
        \\"runtime\\": required field is not set

and remove the following test (as nodejs runtime was deprecated for a while and more importantly we're really testing the API here, not the code):

=== RUN   TestAccAWSLambdaFunction_runtimeValidation_nodeJs
--- FAIL: TestAccAWSLambdaFunction_runtimeValidation_nodeJs (54.41s)
    testing.go:494: Step 0, no error received, but expected a match to:
        
        nodejs has reached end of life since October 2016 and has been deprecated in favor of nodejs4.3
        

They both most likely emerged after merging #2348

[Ninir]

LGTM!

[ghost]

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