blurb/abstract.tex: Change pyafm -> unfold-protein and remove Na+

blurb/abstract.tex: Change pyafm -> unfold-protein and remove Na+

The NaCl data had a small number of noisy unfolding events, which
weren't particularly convincing, so they're not in the final thesis.

Instead of mentioning pyafm here, cut straight to the top-level
unfold-protein package, since that's where the experiment control
happens.