Remove translation from step_script to build_script in custom executor

Overview

Remove the translation added in !2227 (merged) / #26418 (closed) for "step_script" to "build_script". Custom executors would need to accept dynamically generated stage names, e.g. "step_script", "step_release".

Additionally, some translation happens in gitlab rails and needs to be cleaned up too. See gitlab!42010 (merged)

The follow stage is going to be renamed:

old stage name	new stage name (14.0)
build_script	step_script