Remove unnecessary store ability from AuditTrail struct

[itsyaasir]

AuditTrail is only ever used as a top-level shared object via transfer::share_object. It is never wrapped in another struct or stored as a dynamic field, so the store ability serves no purpose and unnecessarily expands the public API surface of the type.

Description of change

Links to any relevant issues

Type of change

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes
• I have updated the CHANGELOG.md, if my changes are significant enough