Remove unnecessary cleanup of AXParameter callbacks

[github-actions]

This is an automatic cherry-pick of 4609395bccd4d07b48601658f1afd85b10c84586

The original PR was #235 with message:

There is no need to unregister AXParameter callbacks. The hash table used for storing them will free its contents in ax_parameter_free().

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• I have performed a self-review of my own code
• I have verified that the code builds perfectly fine on my local system
• I have added tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
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• I have made corresponding changes to the documentation