[lint] Remove workaround for previous gaps in AST walking

[turbolent]

Closes onflow/cadence#4470

Description

onflow/cadence#4471 fixed the AST walking, so the workaround in the unused import analyzer is no longer necessary.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[SupunS]

Thanks for cleaning this up! 🧹