pyafm: Use 'open source' instead of 'FLOSS'

pyafm: Use 'open source' instead of 'FLOSS'

Less jargon, and more consistency (e.g. with my title ;).  The libre
distinction is small, and not particularly critical to this paper.  I
think it is essential that labs let you see their experiment control
software (eakly open source).  Whether or not their license allows for
sharing is less critical, although without significant funding
differences, I expect share-alike software to quickly surpass
no-derivatives software in terms of functionality.