[core] Change unused luautils returns to void types

[claywar]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Removes return values from luautils functions that are not utilized in the existing codebase.

Steps to test these changes

No impact to gameplay, tested instances, battlefields, and various "OnX" functions