Don't define nor use health checks with SNEGs

SNEGs don't use health checks and it's an error to add one in their backend services. 'terraform plan' doesn't detect it, only 'apply'.

modules/net-ilb-l7/README.md

@@ -326,8 +326,10 @@ module "ilb-l7" {
         group          = "my-neg"
         max_rate       = { per_endpoint = 1 }
       }]
+      health_checks = []
     }
   }
+  health_check_configs = {}
   neg_configs = {
     my-neg = {
       cloudrun = {
@@ -343,7 +345,7 @@ module "ilb-l7" {
     subnetwork = var.subnet.self_link
   }
 }
-# tftest modules=1 resources=6
+# tftest modules=1 resources=5
 ```
 
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