r/aws_sns_topic_subscription: Use ForceNew instead of custom logic to reduce chances for panic

[bflad]

Fixes #2557 by removing some duplicate update logic causing panics that would be caught by running the existing error checking already handled on create, e.g.

	if err != nil {
		return err
	}

	if subscriptionHasPendingConfirmation(output.SubscriptionArn) {
		log.Printf("[WARN] Invalid SNS Subscription, received a \"%s\" ARN", awsSNSPendingConfirmationMessage)
		return nil
	}

Tests pass locally for me:

 make testacc TEST=./aws TESTARGS='-run=TestAccAWSSNSTopicSubscription'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSSNSTopicSubscription -timeout 120m
=== RUN   TestAccAWSSNSTopicSubscription_importBasic
--- PASS: TestAccAWSSNSTopicSubscription_importBasic (16.90s)
=== RUN   TestAccAWSSNSTopicSubscription_basic
--- PASS: TestAccAWSSNSTopicSubscription_basic (14.66s)
=== RUN   TestAccAWSSNSTopicSubscription_autoConfirmingEndpoint
--- PASS: TestAccAWSSNSTopicSubscription_autoConfirmingEndpoint (43.09s)
=== RUN   TestAccAWSSNSTopicSubscription_autoConfirmingSecuredEndpoint
--- PASS: TestAccAWSSNSTopicSubscription_autoConfirmingSecuredEndpoint (72.53s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	147.239s

[radeksimko]

LGTM. 👍

I also noticed delivery_policy is not implemented (yet) despite being in the schema, but that's out of the scope of this PR.

[bflad]

This has been released in terraform-provider-aws version 1.7.1. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!