[REM] hr: remove unimported file
[REM] hr: remove unimported file

Leftover of 78ac6de52d690d278fd0cde5476bbeaec86cb124 code about mail gateway was moved to
mail_alias.py but mail_thread.py file was not removed.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo