Change sidebar link from 'Deprecations by Milestone' to 'Removals by Milestone'

• Link to the merge request of the new page:

• Give the MR a descriptive title.

• Link to the merge request that introduced the new page.

The sidebar navigation item leads the visitor to expect the resulting page will show the deprecation announcements by milestone.

Instead, the deprecation announcement is listed under the milestone in which it will be removed.