Cease usage of SDK/Content/Mods directory for asset cooker

[Xymanek]

• It can be used by other things
• We already manipulate DefaultEngine.ini, so we can simply add the ContentForCook directory as an absolute path to [Core.System] Paths, saving us on a junction + some other FS operations

[Xymanek]

No longer relevant with the change to DLC cook (#46)