Revert "Changing csv_reader_py impl to return df from objmode (#918)"

[PokhodenkoSA]

This reverts commit 811e9f0a832d48822bcc91c432b8a2cefdd52102.

[pep8speaks]

Hello @PokhodenkoSA! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file sdc/io/csv_ext.py:

Line 346:32: E231 missing whitespace after ','

[PokhodenkoSA]

Duplicate of #932