Remove reference to new_t_test and new_f_test.

I think I have this one correct now.  Closes 
https://github.com/statsmodels/statsmodels/issues/744

Fixes bad PR https://github.com/statsmodels/statsmodels/pull/747

I didn't rebase but I think that's because I didn't need to.  When I forked my docfix branch, my master was already up to date with upstream/master.  Hopefully I'm understanding things now.

Sorry for the headaches;  I'll make up for it with more important PR's later!