Improve ASP code: get rid of search_new_persistence argument

reported from #15838 (closed)

additionalsoftware.py:

• get_persistence_path(): only ever called with search_new_persistence=True, return_nonexistent=False
• has_unlocked_persistence(): only called with search_new_persistence=True

persistence.py:

• get_persistence_path(): only ever called with search_new_persistence=True, return_nonexistent=False
• has_unlocked_persistence(): only called with search_new_persistence=True

Related issues

• Related to #15838 (closed)
• Related to #14568 (closed)

Original created by @u on 16061 (Redmine)