Doc: Remove backup_id from backup import url and parameter

In the documentation for importing backups the backup_id is removed
because the backup_id is generated after the upload and the user
does not need to provide it. Therefore the request parameter
backup_id has also been removed.

Closes-Bug: #1930526
Change-Id: I49e0adea8fbd97d49f4386b8240320ea2baf3661

api-ref/source/v3/ext-backups.inc

@@ -475,7 +475,7 @@ Response Example
 Import a backup
 ~~~~~~~~~~~~~~~
 
-.. rest_method::  POST /v3/{project_id}/backups/{backup_id}/import_record
+.. rest_method::  POST /v3/{project_id}/backups/import_record
 
 Import information about a backup.
 
@@ -499,7 +499,6 @@ Request
 .. rest_parameters:: parameters.yaml
 
    - project_id: project_id_path
-   - backup_id: backup_id_required
    - backup-record: backup_record
    - backup_service: backup_service
    - backup_url: backup_url