Update Project wikis API page based on initial review

Issue description

This page describes product documentation work that was identified during a documentation review of documentation pages associated with the Create:Editor stage/group.

Page: https://docs.gitlab.com/ee/api/wikis.html

Identified items

• How does a user know what version of the API they're using?
• Fix punctuation in tables.
• On success the HTTP status code in https://docs.gitlab.com/ee/api/wikis.html#delete-a-wiki-page: spell out the name of the HTTP response code.