fix: removing all duplicated variants in sumstats for finemapping functions

[Daniel-Considine]

✨ Context

Some sumstats files have duplicated variant rows, where it isn't clear which is the correct entry. This causes errors in the finemapping pipelines, specifically when extracting the gnomad blockmatrix.

🛠 What does this PR implement

adds a few lines to remove ALL variants that appear more than once in the sumstats prior to finemapping.

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