plpython: Remove duplicate PyModule_Create()

plpython: Remove duplicate PyModule_Create()

This seems to have existed like this since Python 3 support was
added (commit dd4cd55c158), but it's unclear what this second call is
supposed to accomplish.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: li carol <carol.li2025@outlook.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Discussion: https://www.postgresql.org/message-id/f31333f1-fbb7-4098-b209-bf2d71fbd4f3%40eisentraut.org