tests/resource/aws_lb: Remove missing attribute from TestAccAWSLBBackwardsCompatibility

[bflad]

Missed this yesterday in #4032 😓 - the attribute should be missing as it is not applicable to application load balancers.

Previously:

make testacc TEST=./aws TESTARGS='-run=TestAccAWSLBBackwardsCompatibility'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSLBBackwardsCompatibility -timeout 120m
=== RUN   TestAccAWSLBBackwardsCompatibility
--- FAIL: TestAccAWSLBBackwardsCompatibility (212.66s)
	testing.go:518: Step 0 error: Check failed: 1 error(s) occurred:

		* Check 9/16 error: aws_alb.lb_test: Attribute 'enable_cross_zone_load_balancing' not found
FAIL
FAIL	github.com/terraform-providers/terraform-provider-aws/aws	212.707s
make: *** [testacc] Error 1

Now:

make testacc TEST=./aws TESTARGS='-run=TestAccAWSLBBackwardsCompatibility'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSLBBackwardsCompatibility -timeout 120m
=== RUN   TestAccAWSLBBackwardsCompatibility
--- PASS: TestAccAWSLBBackwardsCompatibility (191.09s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	191.136s

[appilon]

Does the suppress function actually remove the fields from TF state?

[bflad]

Hm, I'm actually not sure. Maybe this actually came from the original PR and I just hadn't noticed it amongst the other "usual" test failures.

[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!