[FIX] remove m/z value from required fields

- since mProphet and pyProphet report the m/z value differently ("m.z"
  or "m/z"), delete it completely from the required input fields

git-svn-id: https://msproteomicstools.googlecode.com/svn/trunk@262 db641661-14cc-1e01-c2f8-e77ac6f8a696