MAINT: remove unused attributes from stats.rv_continuous
MAINT: remove attribute aliases from rv_continuous & rv_discrete
BUG: correct vecentropy.nin
DOC: tweak the stats tutorial

Remove a cautionary note which no longer applies.
DEP: stats: deprecate zprob, fprob, ksprob
DOC: stats: mention deprecations in the release notes
MAINT: stats: use/mention stats.XXX.sf methods instead of special.YYY
Merge pull request #3243 from ev-br/distr_cleanup

a bit of maintanence work in stats