fix: revert distinct for associations input file

[vivienho]

✨ Context

I noticed that the gwas associations input file (gs://gwas_catalog_inputs/gwas_catalog_associations_ontology_annotated.tsv) contained duplicate rows, and added a line to drop duplicates after reading the file. This change resulted in an unexpected bug - in the resulting data variantIds were randomly mapped to different studyIds in each run (likely due to pyspark's optimisations). The input file containing duplicates is not really a problem, so I am reverting the initial change in this PR.

🛠 What does this PR implement

Reverts the changes made to drop duplicate rows from the associations input file.

This PR also renames the temporary studyLocusId created using monotonically_increasing_id() to rowId, to distinguish it from the actual studyLocusId assigned at a later stage.

🙈 Missing

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