Build: move unused variable and parameter in gcc from errors to warning

[Xenphis]

Changes Proposed:

This PR proposes changes to:

• Core (units, players, creatures, game systems).
• Scripts (bosses, spell scripts, creature scripts).
• Database (SAI, creatures, etc).

Unused parameters and variables are not important. It will take times before to fix all scripts, so for the moment move them in warnings.

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Issues Addressed:

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