Leave publication
As a writer or editor for a publication, you have the option of leaving that publication. If you do, you will not be able to contribute any more stories, unless you are added again to that publication.
See also: Managing editors and writers
To leave a publication:
Navigate to your publications page through the drop-down menu under your user icon, or go directly to https://medium.com/me/publications:

At the top of your publications list will be any publications you are "Contributing to," as either a writer, editor or owner. The type of contribution will be listed under the name of the publication at left.
You can only leave publications for which you are not the owner.
Click on "Leave publication" on the right to stop contributing to that publication.
A confirmation screen will appear:

Click the button labelled "Confirm."
You will no longer be able to add stories to that publication.
Note: Any stories you've published in that publication will remain in the publication. If you want to remove published stories from a publication, you must do so manually.