Remove fbvscode_traceback fallback and delete benchmark

Summary:
Removes last back-edge from tintype FB wrapper to fbvscode_traceback and deletes benchmark per user choice.

- tintype_debug_launcher.py: Remove _fallback_post_mortem importing offline_post_mortem from fbvscode_traceback, now pure delegate
- BUCK: Remove fbvscode deserialization dep
- DELETE benchmark.py (689 lines) + demo/BUCK — was comparison bench snapshot vs serialization, now last importer deleted
- session.py: docstring cleanup

Reviewed By: aperez

Differential Revision: D114086214

fbshipit-source-id: 531dc082306e1bdf574bcc69194907f225516850

Author: pdepetro

dap/session.py

@@ -114,10 +114,10 @@ def extend_default_exclude_frame_paths(patterns: Iterable[str]) -> None:
     """Append ``patterns`` to :data:`DEFAULT_EXCLUDE_FRAME_PATHS`.
 
     The public tintype module is PyPI-published and can't know about
-    Meta-internal noise (``/sand/``, ``fbvscode_traceback``, etc.).
-    Meta-specific wrappers import this function at module-load time and
-    call it before the DAP server starts, so the augmented list is in
-    place by the time any ``launch`` request is processed.
+    Meta-internal noise (``/sand/``, etc.). Meta-specific wrappers import
+    this function at module-load time and call it before the DAP server
+    starts, so the augmented list is in place by the time any ``launch``
+    request is processed.
 
     This API mutates the module-level list in-place. Callers that
     import ``DEFAULT_EXCLUDE_FRAME_PATHS`` directly will see the