Remove dead code from clinic.py

[erlend-aasland]

There's a bit of unused code in clinic.py. For example, the code that manipulated second_pass_replacements was removed in 2015 (commit 0759f84, gh-67688 (bpo-23500)), but the variable and a branch depending on it still persists.

Suggesting to remove all unused code in order to make clinic more readable and maintainable.

Linked PRs

• gh-104146: Remove unused 'second_pass_replacements' from clinic.py #104147
• gh-104146: Remove unused var 'parser_body_declarations' from clinic.py #104214
• gh-104146: Remove unused vars from Argument Clinic #104627
• gh-104146: Purge dead code from Argument Clinic #104680
• gh-104146: Remove unused attr 'parameter_indent' from clinic.DLParser #106358
• gh-104146: Remove dead code from Argument Clinic #107555
• gh-104146: Argument clinic: remove unused methods and variables #107608
• gh-104146: Argument clinic: Remove dead code flagged by mypy's truthy-bool check #107627
• gh-104146: Argument clinic: remove dead code highlighted by the vulture tool #107632
• gh-104146: Purge CConverter.parse_by_reference from Argument Clinic #119162