TST: anova with `-1` noconstant, add tests

adds unit test for noconstant case for ANOVA

issue #1213 looks outdated, results in examples are the same as in R without changes

where/when was this fixed

AFAIU: `df_model` doesn't know anything about a constant
obviously it does now take implicit constants into account see last comment in #1213 


I'd like to switch to using `df_resid`
I don't trust df_model even if it works correctly in these cases.