Preserve installed_on_request for dependencies

[alyssais]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew tests with your changes locally?

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Fixes #3642.

It would be nice if the Tab returned from for_formula when the formula isn't installed didn't look like a real one that had been installed on request…

Test cases

dd5f216 is the commit before libdvdcss was updated.

export HOMEBREW_BUILD_FROM_SOURCE=1
brew install libdvdread
jq .installed_on_request "$(brew --prefix libdvdcss)/INSTALL_RECEIPT.json"
# should be false

export HOMEBREW_BUILD_FROM_SOURCE=1
export HOMEBREW_NO_AUTO_UPDATE=1
git -C "$(brew --repo homebrew/core)" checkout dd5f216bfe7d8d186853f303fb68cb4c0ecbdba8
brew install libdvdcss
git -C "$(brew --repo homebrew/core)" checkout master
brew install libdvdread
jq .installed_on_request "$(brew --prefix libdvdcss)/INSTALL_RECEIPT.json"
# should be true (this is what is currently broken)

export HOMEBREW_BUILD_FROM_SOURCE=1
export HOMEBREW_NO_AUTO_UPDATE=1
git -C "$(brew --repo homebrew/core)" checkout dd5f216bfe7d8d186853f303fb68cb4c0ecbdba8
brew install libdvdread
brew uninstall libdvdread
git -C "$(brew --repo homebrew/core)" checkout master
brew install libdvdread
jq .installed_on_request "$(brew --prefix libdvdcss)/INSTALL_RECEIPT.json"
# should be true

[MikeMcQuaid]

Looks good, thanks @alyssais! Can you split whitespace-refactoring-only changes into additional commits in future? Makes it easier to review.