Update deprecation/removal docs to point to labels/milestones instead
Update deprecation/removal docs to point to labels/milestones instead

Using milestones and proper issues are a much saner way to handle these topics
than keeping them in sync in a separate document

hackebrot/pytest,markshao/pytest,tareqalayan/pytest,davidszotten/pytest,ddboline/pytest,pytest-dev/pytest,Akasurde/pytest,RonnyPfannschmidt/pytest,nicoddemus/pytest,The-Compiler/pytest,alfredodeza/pytest,pfctdayelise/pytest,nicoddemus/pytest,tomviner/pytest,tomviner/pytest,The-Compiler/pytest,txomon/pytest