REF/TST: Finish pytest idiom in parser tests
Adds more idiom to the following:

* `parser/usecols` --> `parser/test_usecols`
* `parser/quoting` --> `parser/test_quoting`
* `parser/common` --> `parser/test_common`
* `parser/python_parser_only` --> `parser/test_python_parser_only`

Also:

* Finally delete `parser/test_parsers`! 🎉 
* Small bug in `capture_stdout` in which we forgot to use `compat.wraps`.

Builds off of #23712.