[Merged by Bors] - chore(Algebra/Ring): remove variables unused in section

[b-mehta]

Perhaps we should have a linter for this... @adomani?

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[github-actions]

PR summary 8f2d3164d5

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

[adomani]

This seems like a fun linter to write! Environment linters don't know about variables and syntax linters have a hard time persisting information across commands.

I'll try to see if something can be done!

[adomani]

Bhavik, I wrote a linter and these are the first unused variables found: #17261.

There are many more: some are potential false positives, since the linter is not really able to deal with declarations that use the equation compiler, but a lot of the output are actually unused variables.

[adomani]

maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by adomani.

[kim-em]

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• Build
• Lint style