Missing or misplaced test for GLMS?

[jachymb]

The only GLM lpmf/lpdf test in test/unit/math/prim/prob/ seems to be for binomial_logit_lpdf

The other GLMs apparently only have tests in test/unit/math/rev/prob/

Maybe the files just should be split into two? I am not sure.

[WardBrian]

It looks like the rev files are also doing the tests that should belong in prim, if they were following the folder structure exactly