Revert "[ADD] purchase: average price computation test"

This reverts commit 5f9280e8.

These tests have been introduced in 7.0/saas-3, but can no longer be applied in 8.0, as they uses models that do not exist anymore in the new wms.

if such tests do not exist yet in Odoo 8.0, then these tests needs re-work, they cannot be applied like that

Conflicts:
	addons/purchase/tests/test_average_price.py