Remove the BrainGlobe repo renaming functionality

[samcunliffe]

They renamed repos and needed to do some fancy things to make the download counts consistent.

[Copilot]

Pull Request Overview

This PR removes the special-case logic that remapped legacy BrainGlobe package names to current repository names and deletes the associated mapping file. The goal is to simplify conda download aggregation by relying solely on current package/repo names.

• Remove BrainGlobe-specific legacy renaming map usage in addCondaData
• Drop the brainglobe_legacy.json mapping file

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
backend/src/fetchers/fetch_parquet.ts	Removes reading and application of the BrainGlobe legacy package name map and updates aggregation loops to operate only on current package names.
backend/brainglobe_legacy.json	Deletes the legacy package renaming map file no longer used.

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