fix: remove attribute causing issues when bootstrapping cluster

When we set this, Longhorn creates a prototype StorageClass that Argo CD is then unable to update with the configurations desired, giving an error message `The StorageClass "longhorn-backup" is invalid: parameters: Forbidden: updates to parameters are forbidden.`.

Removing the attribute `defaultLonghornStaticStorageClass` removes that problem while maintaining the normal behavior of the module, as the StorageClass is set as default by the annotation `storageclass.kubernetes.io/is-default-class: {{ $.Values.backups.defaultStorageClass | quote }}`.

locals.tf

@@ -12,7 +12,6 @@ locals {
       defaultSettings = {
         backupTarget                      = var.enable_pv_backups ? format("s3://%s@%s/", var.backup_storage.bucket_name, var.backup_storage.region) : ""
         backupTargetCredentialSecret      = var.enable_pv_backups ? "longhorn-s3-secret" : ""
-        defaultLonghornStaticStorageClass = var.enable_pv_backups && var.set_default_storage_class ? "longhorn-backup" : "longhorn-static"
         storageOverProvisioningPercentage = var.storage_over_provisioning_percentage
         storageMinimalAvailablePercentage = var.storage_minimal_available_percentage
         taintToleration                   = join(";", local.tolerations_list)