Consolidate stub helpers and use them consistently

What does this MR do?

I was reading through the code that stubs a basic gitlab CI yaml configuration file, and noticed that we could get rid of a file and use the existing helper more consistently. By using it everywhere, it'll be more easily understood what is happening when the method is invoked. Multiple ways of doing the same thing only ass confusion.

How to setup and validate locally (strongly suggested)

This is just a spec refactoring, so you could run any of the modified specs locally. Really though the way to validate this is with CI passing. No specs or behavior should change.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.