fix: simplify logic for HTTP/1.1 REST fallback option (#54)

* fix: simplify logic for HTTP/1.1 REST fallback option

For the `fallback` parameter, all values considered as `true`
in Boolean context will enable HTTP/1.1 REST fallback,
since the other fallback transport, proto over HTTP, is
removed from `google-gax` v4.

PiperOrigin-RevId: 559812260

Source-Link: googleapis/googleapis@6a6fd29

Source-Link: https://github.com/googleapis/googleapis-gen/commit/56c16657e7a59122b1da94771a9ef40989c282c0
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* 🦉 Updates from OwlBot post-processor

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---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

src/v1/provisioning_client.ts

@@ -98,16 +98,15 @@ export class ProvisioningClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
    *     need to avoid loading the default gRPC version and want to use the fallback
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ProvisioningClient({fallback: 'rest'}, gax);
+   *     const client = new ProvisioningClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -179,7 +178,7 @@ export class ProvisioningClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -238,7 +237,7 @@ export class ProvisioningClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {

src/v1/registry_client.ts

@@ -96,16 +96,15 @@ export class RegistryClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
    *     need to avoid loading the default gRPC version and want to use the fallback
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new RegistryClient({fallback: 'rest'}, gax);
+   *     const client = new RegistryClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class RegistryClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {