Thanks for reaching out. We don't have the ability to remove already run Pipelines from the UI and this isn't something that we're likely to support. The Pipelines page provides a way for users to track all of the Pipelines that have run on their account, and to keep track of their build minutes.
If you find that there is too much clutter on your Pipelines page, you can always fork the repository. Forking the repository does not carry over the already run pipelines.
As an aside, issue #12895 is an open feature request to support testing of the YML configuration before committing it to the repository. You can vote for / watch the issue if it is something that you're interested in seeing.