docs: update service documentation

PiperOrigin-RevId: 567050256

google/cloud/billing/v1/cloud_billing.proto

@@ -88,7 +88,7 @@ service CloudBilling {
   // typically given to billing account
   // [administrators](https://cloud.google.com/billing/docs/how-to/billing-access).
   // This method will return an error if the parent account has not been
-  // provisioned as a reseller account.
+  // provisioned for subaccounts.
   rpc CreateBillingAccount(CreateBillingAccountRequest)
       returns (BillingAccount) {
     option (google.api.http) = {
@@ -290,9 +290,9 @@ message ListBillingAccountsRequest {
   string page_token = 2;
 
   // Options for how to filter the returned billing accounts.
-  // Currently this only supports filtering for
+  // This only supports filtering for
   // [subaccounts](https://cloud.google.com/billing/docs/concepts) under a
-  // single provided reseller billing account.
+  // single provided parent billing account.
   // (e.g. "master_billing_account=billingAccounts/012345-678901-ABCDEF").
   // Boolean algebra and other fields are not currently supported.
   string filter = 3;