beta_binomial default link doc vs summary mismatch

[avehtari]

Tested with the latest github version

Doc says

     beta_binomial(link = "logit", link_phi = "log")

Summary for

fit <- brm(y | trials(n) ~ 1, family=beta_binomial(), data = data.frame(y=1, n=2), iter=1)

says

  Links: mu = logit; phi = identity 

The same issue is at least for zero_inflated_beta_binomial(), too.

So I was confused "log" changing to "identity", but @paul-buerkner reminded that, in my model, phi was not predicted, and thus there was no link function. After discussion, a potential improvement is to not show link for non-predicted distributional parameters, that is for the above case show

  Links: mu = logit