Pagination: do not add `?{page,per_page} parameters for list endpoints only supporting `?since`

[gr2m]

Follow up to https://github.com/octokit/rest.js/issues/1684#issuecomment-617998848

Example, but there are many

• endpoint scope: Repos
• endpoint name: List public repositories
• route: GET /repositories
• documentation URL: https://developer.github.com/v3/repos/#list-public-repositories

We can look for this note:

Note: Pagination is powered exclusively by the since parameter. Use the Link header to get the URL for the next page of repositories.

Current specification

https://github.com/octokit/routes/blob/661f84ec6a5d4265496b3b87680f7664f98ba6fe/openapi/api.github.com/operations/repos/list-public.json#L27-L38

I expected

per_page and page parameters should not be present