code: @BetaApi
    public final Operation deleteRegionDisk(ProjectRegionDiskName disk) {
  
      DeleteRegionDiskHttpRequest request =
          DeleteRegionDiskHttpRequest.newBuilder()
              .setDisk(disk == null ? null : disk.toString())
              .build();
      return deleteRegionDisk(request);
    }
docs: Deletes the specified regional persistent disk. Deleting a regional disk removes all the
  replicas of its data permanently and is irreversible. However, deleting a disk does not delete
  any snapshots previously made from the disk. You must separately delete snapshots.
  
  <p>Sample code:
  
  <pre><code>
  try (RegionDiskClient regionDiskClient = RegionDiskClient.create()) {
  ProjectRegionDiskName disk = ProjectRegionDiskName.of("[PROJECT]", "[REGION]", "[DISK]");
  Operation response = regionDiskClient.deleteRegionDisk(disk);
  }
  </code></pre>
  
  @param disk Name of the regional persistent disk to delete.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails