ECredentialsPrompter: Remove GSimpleAsyncResult from the public API
- ECredentialsPrompter: Use more g_clear_* macros
Allows to make sure that we are not leaving the old pointer/integer in place.
- ECredentialsPrompter: Remove e_credentials_prompter_complete_prompt_call
Untangle the code around GSimpleAsyncResult a bit.
- ECredentialsPrompter: Make e_credentials_prompter_complete_prompt_call private
This method is not used by any consumer and is revealing implementation details of the object.