Remove displacement field from engines

[Milopetilo]

Summary

None

Purpose of change

Removing the old displacement field from engines, which has only been used for generating the volume prefix of the engine name since #65414.
Caught this while testing #71251.

Describe the solution

Removing displacement from engines and instead adding it directly to the name.
Also added a space between the value and unit.

Describe alternatives you've considered

Keeping it in case it's still needed somewhere I didn't catch.

Testing

Started the game up and saw the changes.

Additional context