Engine configured to not import still imports

Given:
engines.<alias>.importEnabled is set to false

When:
I run Optimize

Then:
Import is still performed from the engine with <alias>

Expected:
Import should not be performed from that engine.

AT:

• the issue is fixed and covered properly by tests
• the issue is listed under known issues for 3.0.0
  • needs to get merged to the latest and 3.0 branch of the docs as well