Remove unused instance variables in API code

[dduugg]

Removes instance-variable assignments that are never read.

• In Homebrew::API::JSONDownloadStrategy and Homebrew::API::JSONDownload, @stale_seconds and @target are assigned in initialize but never read (not in these classes, nor in the AbstractDownloadStrategy parent or Downloadable mixin). The value is used through meta[:target]/meta[:stale_seconds] and the target/stale_seconds arguments instead. With both ivars gone, JSONDownloadStrategy#initialize only called super, so it is removed too.
• APIHashable#@old_homebrew_cellar is saved in generating_hash! but never restored anywhere (only @old_homebrew_prefix, @old_home and @old_git_config_global are restored, and HOMEBREW_CELLAR is not monkeypatched in the first place).

Instance-variable assignments like these aren't reported by brew deadcode (Spoom models methods and constants, not ivars), which is why they lingered. Verified with git grep that nothing reads them.

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Claude (Claude Code) found the initial write-only instance variables (@stale_seconds, @old_homebrew_cellar) and drafted the removal. The @target removal was prompted by Copilot's review. I verified with git grep that nothing reads them and ran brew lgtm (style, typecheck, tests) successfully.

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[Copilot]

Pull request overview

This PR removes write-only instance-variable assignments in Homebrew’s API-related code to reduce dead state and keep the API implementation easier to reason about.

Changes:

• Removes unused @stale_seconds assignments from Homebrew::API::JSONDownloadStrategy and Homebrew::API::JSONDownload.
• Removes unused @old_homebrew_cellar capture from APIHashable#generating_hash!.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/api/json_download.rb	Drops unused @stale_seconds ivars in JSON API download strategy/helper classes.
Library/Homebrew/api_hashable.rb	Removes unused @old_homebrew_cellar assignment during API hash generation monkeypatch setup.

Comments suppressed due to low confidence (1)

Library/Homebrew/api/json_download.rb:42

• @target is assigned but never read (this class delegates the target to the URL specs/downloader). Keeping an unused instance variable here is inconsistent with the PR’s goal of removing write-only ivars.

      def initialize(url, target:, stale_seconds:)
        super()
        @url = T.let(URL.new(url, using: API::JSONDownloadStrategy, target:, stale_seconds:), URL)
        @target = target
      end

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[MikeMcQuaid]

Thanks!