[mod] Revert changes made for Poetry 1.0.0b3 now fixed in b4:

- 'poetry run' no longer needs `--`.

Revert "[fix] Call 'poetry run silkaj' tests with '--'"
Revert "[fix] 'poetry run' cli parsing changed in 1.0.0b3:"

This reverts commit f335a2bd.
This reverts commit 4f772671.