simplify exists function, add delete docstring
simplify exists function, add delete docstring

biocore/qiita,squirrelo/qiita,RNAer/qiita,biocore/qiita,antgonza/qiita,josenavas/QiiTa,biocore/qiita,biocore/qiita,squirrelo/qiita,squirrelo/qiita,ElDeveloper/qiita,ElDeveloper/qiita,squirrelo/qiita,josenavas/QiiTa,RNAer/qiita,adamrp/qiita,adamrp/qiita,ElDeveloper/qiita,wasade/qiita,RNAer/qiita,antgonza/qiita,antgonza/qiita,josenavas/QiiTa,adamrp/qiita,wasade/qiita,josenavas/QiiTa,adamrp/qiita,antgonza/qiita,RNAer/qiita,ElDeveloper/qiita,wasade/qiita