Rename Packages::Package#original_build_info to last_build_info

Context

In #365828 (closed) we changed the method #original_build_info to return the most recent pipeline.

What does this MR do and why?

This MR renames #original_build_info to #last_build_info since it reflects better the purpose of method.

Screenshots or screen recordings

No.

How to set up and validate locally

In rails console

1. Create a new instance of Packages::BuildInfo class

   i = FactoryBot.create(:package_build_info)

2. Get the linked package from the build info

   p = i.package

3. Call #last_build_info on the package and check the output

   p.last_build_info

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #410352 (closed)