Refactor CI includes

What does this MR do and why?

This MR is based on !111450 (merged)

This MR is mostly about removing redundant controls.

• Removed next unless artifact_job from Artifact#content because this method will not be called if it is not valid.
• Removed next unless creating_child_pipeline? from Artifact#content because this method will not be called if it is not valid.
• Replaced return unless context.project with return unless valid? in the Local#masked_* methods because we don't need those methods unless valid.
• Removed next unless can_access_local_content? and return unless sha from Project#fetch_local_content because this method will not be called if it is not valid.
• Removed next unless project from Project#sha because this method will not be called if it is not valid.
• Replaced return unless project with valid? in the Project#masked_* methods because we don't need those methods unless valid.

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.