Remove dangerous sys.path manipulations in test_pluginmanager
Remove dangerous sys.path manipulations in test_pluginmanager

Noticed these while working in something else

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