Remove reads to stage column from build

Ref: #364377

What does this MR do and why?

This MR removes reads to ci_build.stage column since we want to remove that column because the data is now stored in ci_stage.

We are setting up the association between Ci:Build & Ci::Stage named ci_stage so it does not conflict with the stage column until we are able to remove it.

This work is actually the first step of this implementation:

Step	Status
1. Remove read from ci_builds.stage	👈 You are here
2. Drop Ci::EnsureStageService	#364377
3. Ignore column & drop the column	#364377

This is Step # 1 in order to remove ci_builds.stage column.

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