remove some support code for old python versions
remove some support code for old python versions

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