clear_sync
Description:
public bool clear_sync (Schema? schema, HashTable<string,string> attributes, Cancellable? cancellable = null) throws Error
  
  Remove unlocked items which match the attributes from the secret service.
The attributes should be a set of key and value string pairs.
If this is null, then [funcService.get_sync] will be called to get the default
      [classService] proxy.
This method may block indefinitely and should not be used in user interface threads.
Parameters:
| this | the secret service | 
| schema | the schema for the attributes | 
| attributes | the attribute keys and values | 
| cancellable | optional cancellation object | 
Returns:
| whether items were removed or not |