[easy] DRY in Parsing_heaps
[easy] DRY in Parsing_heaps

Summary: makes `get_ast_unsafe` call `get_ast` (similar for the others), instead of reimplementing it

Reviewed By: samwgoldman

Differential Revision: D24487000

fbshipit-source-id: 8934ec394bcb0c8e9aa38be96056fb6dd27eeca2

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow